Predict future periods, ovulation dates and fertile windows.
Menstrual Cycle Calculator predicts future menstrual cycles, fertile windows, and ovulation dates based on cycle history and patterns.
Try it — live request, no key required
GETapi.apiverve.com/v1/menstrualcycle?last_period=2024-01-01
Query parametersVerificationFormat
No key required to try it. Get a key to use it in your app.
{
"status": "ok",
"error": null,
"data": {
"last_period_date": "2024-01-01",
"cycle_length": 28,
"period_length": 5,
"cycles_calculated": 3,
"cycles": [
{
"cycle_number": 1,
"period": {
"start_date": "2024-01-01",
"end_date": "2024-01-05",
"duration_days": 5
},
"ovulation": {
"date": "2024-01-15",
"day_of_cycle": 14
},
"fertile_window": {
"start_date": "2024-01-10",
"end_date": "2024-01-15",
"duration_days": 6
},
"pms_phase": {
"start_date": "2023-12-21",
"end_date": "2023-12-31"
},
"cycle_phases": {
"menstrual": {
"start": "2024-01-01",
"end": "2024-01-05",
"description": "Menstruation"
},
"follicular": {
"start": "2024-01-06",
"end": "2024-01-14",
"description": "Follicular phase - preparing for ovulation"
},
"ovulation": {
"date": "2024-01-15",
"description": "Ovulation - most fertile day"
},
"luteal": {
"start": "2024-01-16",
"end": "2024-01-28",
"description": "Luteal phase - preparing for next period"
}
},
"status": "past",
"days_until": null,
"days_ago": 715
},
{
"cycle_number": 2,
"period": {
"start_date": "2024-01-29",
"end_date": "2024-02-02",
"duration_days": 5
},
"ovulation": {
"date": "2024-02-12",
"day_of_cycle": 14
},
"fertile_window": {
"start_date": "2024-02-07",
"end_date": "2024-02-12",
"duration_days": 6
},
"pms_phase": {
"start_date": "2024-01-18",
"end_date": "2024-01-28"
},
"cycle_phases": {
"menstrual": {
"start": "2024-01-29",
"end": "2024-02-02",
"description": "Menstruation"
},
"follicular": {
"start": "2024-02-03",
"end": "2024-02-11",
"description": "Follicular phase - preparing for ovulation"
},
"ovulation": {
"date": "2024-02-12",
"description": "Ovulation - most fertile day"
},
"luteal": {
"start": "2024-02-13",
"end": "2024-02-25",
"description": "Luteal phase - preparing for next period"
}
},
"status": "past",
"days_until": null,
"days_ago": 687
},
{
"cycle_number": 3,
"period": {
"start_date": "2024-02-26",
"end_date": "2024-03-01",
"duration_days": 5
},
"ovulation": {
"date": "2024-03-11",
"day_of_cycle": 14
},
"fertile_window": {
"start_date": "2024-03-06",
"end_date": "2024-03-11",
"duration_days": 6
},
"pms_phase": {
"start_date": "2024-02-15",
"end_date": "2024-02-25"
},
"cycle_phases": {
"menstrual": {
"start": "2024-02-26",
"end": "2024-03-01",
"description": "Menstruation"
},
"follicular": {
"start": "2024-03-02",
"end": "2024-03-10",
"description": "Follicular phase - preparing for ovulation"
},
"ovulation": {
"date": "2024-03-11",
"description": "Ovulation - most fertile day"
},
"luteal": {
"start": "2024-03-12",
"end": "2024-03-24",
"description": "Luteal phase - preparing for next period"
}
},
"status": "past",
"days_until": null,
"days_ago": 659
}
],
"current_status": {
"phase": "Unknown",
"description": "",
"next_period": null,
"days_until_next_period": null
},
"averages": {
"cycle_length": 28,
"period_duration": 5,
"days_between_periods": 28
},
"disclaimer": "This calculator provides estimates only. Actual cycles may vary. Consult a healthcare provider for medical advice."
}
}
About the Menstrual Cycle Calculator API
Provides current cycle status, PMS timing, and comprehensive period tracking information, perfect for women's health apps and cycle monitoring applications.
What people use it for
- Period Tracking
- Build period tracking applications with accurate cycle predictions, period start dates, and phase identification
- Cycle Prediction
- Predict future menstrual cycles with customizable cycle length and period duration for planning and preparation
- Health Monitoring
- Create women's health monitoring tools with detailed cycle phase information including follicular, ovulation, and luteal phases
- Health Insights
- Provide cycle-based health insights and symptom tracking aligned with menstrual phases for better health awareness
Ways to call it
One endpoint, many ways in — REST with JSON, XML, YAML and CSV, plus GraphQL and an MCP interface for AI agents.
- JSON
- Default REST response
- XML
- Markup format
- YAML
- Human-readable
- CSV
- Tabular export
- GraphQL
- Query language
- MCP
- For AI agents
Beta
New
Other ways to use Menstrual Cycle Calculator
Same data, same APIVerve account, same credit balance — one key works on all of them.
Give it to an AI agentConnect over MCP and your agent calls it as a native tool — Claude, Cursor, ChatGPT.on VerveKit Google Sheets or ExcelA =VERVE() formula fills a column — no script, no export, recalculates in place.on VerveSheets Ground an agent on itA cited, machine-checkable fact your model can't produce on its own.on VerveContext
Which plan fits 25,000 cycle calculations a month?
Starter easily covers that volume. Each call uses 2 credits, so 25,000 calculations take 50,000 credits, leaving three-quarters of Starter's 200,000 monthly credits available. That works out to about $0.30 per 1,000 calls. The Free plan provides 100 calls each month for development and testing.
Are phase breakdowns and PMS timing included on the Free plan?
No. Detailed cycle phases (menstrual, follicular, ovulation, luteal), PMS phase dates, current cycle status, and historical cycle averages are premium fields. Any paid plan unlocks them. The Free plan returns period dates, estimated ovulation day, and fertile windows.
Can I project multiple upcoming cycles in a single call?
Yes. Passing the cycles parameter lets you generate forecasts across multiple consecutive cycles. Menstrual Cycle Calculator returns each future cycle in sequence with its own period start and end dates, estimated ovulation day, and fertile window.
Can I customize the cycle and period duration for each user?
Yes. You can supply custom values for cycle length and period duration in days. The calculations adjust all projected period dates, ovulation estimates, and fertile windows to reflect that user's specific cycle pattern.
What date format must I provide for the last period?
The last_period parameter requires a YYYY-MM-DD string representing the first day of the user's most recent menstrual period. It is the only required input needed to generate cycle predictions.
Request parameters — GET /v1/menstrualcycle
Sent in the query string. Premium parameters are accepted on every plan but only take effect on plans that include them. Anything not listed here is dropped rather than passed through.
Required
| Parameter | Type | Example | Description |
|---|---|---|---|
last_periodRequired | string | 2024-01-01 | First day of last menstrual period (YYYY-MM-DD) date |
Optional
| Parameter | Type | Example | Description |
|---|---|---|---|
cycle_lengthOptional | integer | 28 | Average cycle length in days default 28 · range 21-35 |
period_lengthOptional | integer | 5 | Average period duration in days default 5 · range 2-10 |
cyclesOptional | integer | 3 | Number of future cycles to calculate default 3 · range 1-12 |
curl "https://api.apiverve.com/v1/menstrualcycle?last_period=2024-01-01&cycle_length=28&period_length=5&cycles=3" \
-H "x-api-key: YOUR_API_KEY"Authentication
Send your key in the x-api-key header. That is the only auth step — no token exchange, and no per-endpoint scope to configure.
| Header | When | Value |
|---|---|---|
x-api-keyRequired | Every request | Your API key. Header names are case-insensitive, so X-API-Key is the same header. |
AuthorizationAlternate | Instead of the above | Bearer <key> — for clients that only expose bearer auth. Resolves to the same account and the same billing. |
401 is the only auth verdict
A 401 means the key is missing, invalid or expired. A 403 means the key is valid but not permitted here — blocked by a key restriction or an IP allow-list. Running out of credits is a 429.
Response — GET /v1/menstrualcycle
Every APIVerve endpoint returns the same three top-level keys, so one response handler covers your whole integration: status, error and data. Only data changes shape.
{
"status": "ok",
"error": null,
"data": {
"last_period_date": "2024-01-01",
"cycle_length": 28,
"period_length": 5,
"cycles_calculated": 3,
"cycles": [
{
"cycle_number": 1,
"period": {
"start_date": "2024-01-01",
"end_date": "2024-01-05",
"duration_days": 5
},
"ovulation": {
"date": "2024-01-15",
"day_of_cycle": 14
},
"fertile_window": {
"start_date": "2024-01-10",
"end_date": "2024-01-15",
"duration_days": 6
},
"pms_phase": {
"start_date": "2023-12-21",
"end_date": "2023-12-31"
},
"cycle_phases": {
"menstrual": {
"start": "2024-01-01",
"end": "2024-01-05",
"description": "Menstruation"
},
"follicular": {
"start": "2024-01-06",
"end": "2024-01-14",
"description": "Follicular phase - preparing for ovulation"
},
"ovulation": {
"date": "2024-01-15",
"description": "Ovulation - most fertile day"
},
"luteal": {
"start": "2024-01-16",
"end": "2024-01-28",
"description": "Luteal phase - preparing for next period"
}
},
"status": "past",
"days_until": null,
"days_ago": 715
},
{
"cycle_number": 2,
"period": {
"start_date": "2024-01-29",
"end_date": "2024-02-02",
"duration_days": 5
},
"ovulation": {
"date": "2024-02-12",
"day_of_cycle": 14
},
"fertile_window": {
"start_date": "2024-02-07",
"end_date": "2024-02-12",
"duration_days": 6
},
"pms_phase": {
"start_date": "2024-01-18",
"end_date": "2024-01-28"
},
"cycle_phases": {
"menstrual": {
"start": "2024-01-29",
"end": "2024-02-02",
"description": "Menstruation"
},
"follicular": {
"start": "2024-02-03",
"end": "2024-02-11",
"description": "Follicular phase - preparing for ovulation"
},
"ovulation": {
"date": "2024-02-12",
"description": "Ovulation - most fertile day"
},
"luteal": {
"start": "2024-02-13",
"end": "2024-02-25",
"description": "Luteal phase - preparing for next period"
}
},
"status": "past",
"days_until": null,
"days_ago": 687
},
{
"cycle_number": 3,
"period": {
"start_date": "2024-02-26",
"end_date": "2024-03-01",
"duration_days": 5
},
"ovulation": {
"date": "2024-03-11",
"day_of_cycle": 14
},
"fertile_window": {
"start_date": "2024-03-06",
"end_date": "2024-03-11",
"duration_days": 6
},
"pms_phase": {
"start_date": "2024-02-15",
"end_date": "2024-02-25"
},
"cycle_phases": {
"menstrual": {
"start": "2024-02-26",
"end": "2024-03-01",
"description": "Menstruation"
},
"follicular": {
"start": "2024-03-02",
"end": "2024-03-10",
"description": "Follicular phase - preparing for ovulation"
},
"ovulation": {
"date": "2024-03-11",
"description": "Ovulation - most fertile day"
},
"luteal": {
"start": "2024-03-12",
"end": "2024-03-24",
"description": "Luteal phase - preparing for next period"
}
},
"status": "past",
"days_until": null,
"days_ago": 659
}
],
"current_status": {
"phase": "Unknown",
"description": "",
"next_period": null,
"days_until_next_period": null
},
"averages": {
"cycle_length": 28,
"period_duration": 5,
"days_between_periods": 28
},
"disclaimer": "This calculator provides estimates only. Actual cycles may vary. Consult a healthcare provider for medical advice."
}
}
Response fields
Paths are relative to data. Premium fields are absent rather than zeroed on plans that do not include them, so check for presence instead of comparing to 0.
| Field | Type | Example | Description |
|---|---|---|---|
last_period_date | string | "2024-01-01" | First day of last menstrual period |
cycle_length | number | 28 | Average menstrual cycle length in days |
period_length | number | 5 | Average menstrual period duration in days |
cycles_calculated | number | 3 | Total number of cycles calculated |
cycles | array[3] | Array of calculated menstrual cycles with details | |
cycle_number | number | 1 | Sequential number of the cycle |
period | object | {...} | Start, end and length of the period for this cycle |
start_date | string | "2024-01-01" | Start date of menstrual period |
end_date | string | "2024-01-05" | End date of menstrual period |
duration_days | number | 5 | Duration of period in days |
ovulation | object | {...} | Estimated ovulation date and which day of the cycle it falls on |
date | string | "2024-01-15" | Predicted ovulation date in cycle |
day_of_cycle | number | 14 | Day of cycle when ovulation occurs |
fertile_window | object | {...} | Range of days conception is possible in this cycle |
start_date | string | "2024-01-10" | Start of fertile window for conception |
end_date | string | "2024-01-15" | End of fertile window for conception |
duration_days | number | 6 | Duration of fertile window in days |
pms_phase | object | {...} | Range of days premenstrual symptoms are expected |
start_datePremium | string | "2023-12-21" | Start date of PMS phase |
end_datePremium | string | "2023-12-31" | End date of PMS phase |
cycle_phasesPremium | object | {...} | Detailed breakdown of menstrual cycle phases |
menstrualPremium | object | {...} | The bleeding phase, with its dates |
startPremium | string | "2024-01-01" | Start date of menstrual phase |
endPremium | string | "2024-01-05" | End date of menstrual phase |
descriptionPremium | string | "Menstruation" | Description of menstrual phase |
follicularPremium | object | {...} | From the end of the period to ovulation |
startPremium | string | "2024-01-06" | Start date of follicular phase |
endPremium | string | "2024-01-14" | End date of follicular phase |
descriptionPremium | string | "Follicular phase - preparing for ovulation" | Description of follicular phase |
ovulationPremium | object | {...} | The day the egg is released |
datePremium | string | "2024-01-15" | Ovulation date within cycle |
descriptionPremium | string | "Ovulation - most fertile day" | Description of ovulation phase |
lutealPremium | object | {...} | From ovulation to the start of the next period |
startPremium | string | "2024-01-16" | Start date of luteal phase |
endPremium | string | "2024-01-28" | End date of luteal phase |
descriptionPremium | string | "Luteal phase - preparing for next period" | Description of luteal phase |
statusPremium | string | "past" | Status of cycle relative to current date |
days_untilPremium | object | null | Days until cycle phase occurs |
days_agoPremium | number | 715 | Days since cycle phase occurred |
current_status | object | {...} | Which phase today falls in and when the next period is due |
phasePremium | string | "Unknown" | Current menstrual cycle phase name |
descriptionPremium | string | "" | Description of current cycle phase |
next_periodPremium | object | null | Date of next expected menstrual period |
days_until_next_periodPremium | object | null | Days until next menstrual period starts |
averages | object | {...} | Average cycle length, period duration and gap between periods |
cycle_lengthPremium | number | 28 | Average menstrual cycle length across periods |
period_durationPremium | number | 5 | Average menstrual period duration across cycles |
days_between_periodsPremium | number | 28 | Average days between menstrual period starts |
disclaimer | string | "This calculator provides estimates only. Actual cycles may vary. Consult a healthcare provider for medical advice." | Legal disclaimer about calculation accuracy |
Response headers
Every response carries your balance, so your own code always knows where it stands without polling anything. All four are exposed to browsers through CORS.
| Header | What it carries |
|---|---|
x-api-remaining-credits | Credits left in the current cycle |
x-api-credits-used | Credits spent in the current cycle |
x-api-max-credits | The allowance for the cycle |
x-api-version | Version of the endpoint that answered |
Errors
Read the HTTP status first, then error for the specific reason. The body names the parameter that has to change.
| Status | Meaning | What to do |
|---|---|---|
400 | Input was rejected | Read error; it names the parameter that has to change. |
401 | Key missing or invalid | Check the header name and the key value. |
403 | Key valid, but not permitted here | A key restriction or an IP allow-list — never a bad key. |
429 | Rate limited, or out of credits | Read error to tell them apart, then back off or top up. |
What a call costs — 2 credits per call
Credits are shared across every APIVerve API — one balance, one key, one bill. Failed requests never count against it, so a rejected input costs nothing.
| Plan | Per month | Credits | Menstrual Cycle Calculator calls | Per 1,000 calls |
|---|---|---|---|---|
| Free | Free | 200 | 100 | Free |
| Starter | $29.99 | 200,000 | 100,000 | $0.30 |
| Pro | $99.99 | 1,000,000 | 500,000 | $0.20 |
| Mega | $299.99 | 4,000,000 | 2,000,000 | $0.15 |
Calls are what the credits buy at this API's rate — spend them here, on any of the other APIs, or across both. Nothing is reserved per endpoint.
Call it from cURL — GET /v1/menstrualcycle
No SDK to install — this is a plain HTTPS call to /v1/menstrualcycle with your key in the x-api-key header. Swap in a real key and it runs as-is.
curl "https://api.apiverve.com/v1/menstrualcycle" \
-H "x-api-key: YOUR_API_KEY"Resources
GitHubapiverve/menstrualcycle-apiSource, issues and the examples this page is built from.ReferenceMenstrual Cycle Calculator API docsEvery parameter, every response field, and the errors.ParametersWhat this call acceptsRequired and optional inputs, with example values.
Also published for
Only the languages APIVerve ships a client for are listed — the rest call the endpoint directly over HTTPS.
Call it from Node.js — GET /v1/menstrualcycle
Install the Node.js SDK, then call the Menstrual Cycle Calculator API with your key. The client wraps the same HTTPS request, so anything it returns is what the endpoint returns.
npm install @apiverve/menstrualcycleconst res = await fetch("https://api.apiverve.com/v1/menstrualcycle", {
headers: { "x-api-key": "YOUR_API_KEY" },
});
const { data } = await res.json();
console.log(data);Resources
npm@apiverve/menstrualcycleThe published Node.js client, versioned and signed.GitHubapiverve/menstrualcycle-apiSource, issues and the examples this page is built from.ReferenceMenstrual Cycle Calculator API docsEvery parameter, every response field, and the errors.ParametersWhat this call acceptsRequired and optional inputs, with example values.
Also published for
Only the languages APIVerve ships a client for are listed — the rest call the endpoint directly over HTTPS.
Call it from Python — GET /v1/menstrualcycle
No SDK to install — this is a plain HTTPS call to /v1/menstrualcycle with your key in the x-api-key header. Swap in a real key and it runs as-is.
import requests
res = requests.get(
"https://api.apiverve.com/v1/menstrualcycle",
headers={"x-api-key": "YOUR_API_KEY"},
)
print(res.json()["data"])Resources
GitHubapiverve/menstrualcycle-apiSource, issues and the examples this page is built from.ReferenceMenstrual Cycle Calculator API docsEvery parameter, every response field, and the errors.ParametersWhat this call acceptsRequired and optional inputs, with example values.
Also published for
Only the languages APIVerve ships a client for are listed — the rest call the endpoint directly over HTTPS.
Call it from C# / .NET — GET /v1/menstrualcycle
Install the C# / .NET SDK, then call the Menstrual Cycle Calculator API with your key. The client wraps the same HTTPS request, so anything it returns is what the endpoint returns.
dotnet add package APIVerve.API.MenstrualCycleCalculatorusing var client = new HttpClient();
client.DefaultRequestHeaders.Add("x-api-key", "YOUR_API_KEY");
var json = await client.GetStringAsync("https://api.apiverve.com/v1/menstrualcycle");
Console.WriteLine(json);Resources
NuGetAPIVerve.API.MenstrualCycleCalculatorThe published C# / .NET client, versioned and signed.GitHubapiverve/menstrualcycle-apiSource, issues and the examples this page is built from.ReferenceMenstrual Cycle Calculator API docsEvery parameter, every response field, and the errors.ParametersWhat this call acceptsRequired and optional inputs, with example values.
Also published for
Only the languages APIVerve ships a client for are listed — the rest call the endpoint directly over HTTPS.
Call it from Go — GET /v1/menstrualcycle
No SDK to install — this is a plain HTTPS call to /v1/menstrualcycle with your key in the x-api-key header. Swap in a real key and it runs as-is.
req, _ := http.NewRequest("GET", "https://api.apiverve.com/v1/menstrualcycle", nil)
req.Header.Set("x-api-key", "YOUR_API_KEY")
res, _ := http.DefaultClient.Do(req)
defer res.Body.Close()
body, _ := io.ReadAll(res.Body)
fmt.Println(string(body))Resources
GitHubapiverve/menstrualcycle-apiSource, issues and the examples this page is built from.ReferenceMenstrual Cycle Calculator API docsEvery parameter, every response field, and the errors.ParametersWhat this call acceptsRequired and optional inputs, with example values.
Also published for
Only the languages APIVerve ships a client for are listed — the rest call the endpoint directly over HTTPS.
Call it from PHP — GET /v1/menstrualcycle
No SDK to install — this is a plain HTTPS call to /v1/menstrualcycle with your key in the x-api-key header. Swap in a real key and it runs as-is.
$ch = curl_init("https://api.apiverve.com/v1/menstrualcycle");
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_HTTPHEADER, ["x-api-key: YOUR_API_KEY"]);
$response = curl_exec($ch);
echo $response;Resources
GitHubapiverve/menstrualcycle-apiSource, issues and the examples this page is built from.ReferenceMenstrual Cycle Calculator API docsEvery parameter, every response field, and the errors.ParametersWhat this call acceptsRequired and optional inputs, with example values.
Also published for
Only the languages APIVerve ships a client for are listed — the rest call the endpoint directly over HTTPS.
Call it from Ruby — GET /v1/menstrualcycle
No SDK to install — this is a plain HTTPS call to /v1/menstrualcycle with your key in the x-api-key header. Swap in a real key and it runs as-is.
require "net/http"
uri = URI("https://api.apiverve.com/v1/menstrualcycle")
req = Net::HTTP::Get.new(uri)
req["x-api-key"] = "YOUR_API_KEY"
res = Net::HTTP.start(uri.hostname, uri.port, use_ssl: true) { |h| h.request(req) }
puts res.bodyResources
GitHubapiverve/menstrualcycle-apiSource, issues and the examples this page is built from.ReferenceMenstrual Cycle Calculator API docsEvery parameter, every response field, and the errors.ParametersWhat this call acceptsRequired and optional inputs, with example values.
Also published for
Only the languages APIVerve ships a client for are listed — the rest call the endpoint directly over HTTPS.
Zero-code embed — one snippet, no backend
Drop an interactive Menstrual Cycle Calculator form onto any page. The widget calls the API for you, so no key ever appears in your markup and there is nothing to deploy.
Loading preview…
Changelog — Menstrual Cycle Calculator API
Every change to this endpoint, newest first. Breaking changes ship as a new version and the previous one keeps serving — response fields are added, never removed or retyped in place, so an integration written against v1 keeps working.
Nothing recorded yet
Entries are picked up from dated catalog snapshots, so the first one appears after the next snapshot that moves something. A period where nothing changed produces no entry — silence is a valid changelog for the Menstrual Cycle Calculator API.
More in this category
Lifestyle
- Due Date Calculator
- Menstrual Cycle Calculator
- Ovulation Calculator
Browse by category
Finance 50Text Processing 45Data Conversion 33Data Generation 32Entertainment 24Games 21Domain Data 18Data Lookup 17Networking 14Geography 13Reference Data 11Data Validation 9Weather 9Math/Calculations 8Images 7AI/Computer Vision 6Astrology 6Data Processing 6Transportation 6Data Scraping 5Calendar 5Security 4Science 4Parsers 4Documents 3Food 3Health/Wellness 2News 1All 369 APIs →
Related articles
All articles →
Extract Clean Content from Any WebpageTurn messy web pages into clean Markdown. Perfect for content migration, archiving, AI training data, and building read-later tools.Read 
Take Your App Multilingual (No Rewrite)Add language support to an existing app without rearchitecting. Practical strategies for translation, detection, and localization.Read 
Business Day Math Is Harder Than You ThinkWeekends, holidays, and country-specific rules make working day calculations surprisingly tricky. Here's what to watch for.Read