Due Date Calculator: API and MCP

Due Date Calculator over REST and MCP: input fields, limits, outputs, one example request and its real answer. Free, no sign-up.

Id: health.due-date
Version: 1.0.0
Access: Free
Tool page: Due Date Calculator
Schema: GET /api/v1/tools/health.due-date

Input

Field	Type	Constraints	Default	Description
`method`	string	last-period \| conception \| ivf	last-period	Calculate from
`lastPeriod`	string			First day of the last period
`cycleLength`	integer	≥ 20, ≤ 44	28	Cycle length (days) · Days from the first day of one period to the first day of the next. Leave 28 if you do not know.
`conception`	string			Conception date
`transfer`	string			Embryo transfer date
`embryo`	string	day-5 \| day-3	day-5	Embryo age
`on`	string			Week of pregnancy on · Leave it empty to use today (Türkiye time).

Output

Field	Type	Description
`dueDate`	string	Estimated due date
`weeks`	number	Weeks pregnant (weeks)
`days`	number	Days after the full weeks (days)
`trimester`	number	Trimester
`conceptionDate`	string	Estimated conception date
`daysLeft`	number	Days to the due date (days)
`pregnancyDays`	number	Days pregnant (days)

Example request

curl -X POST https://hesaplayici.com/api/v1/tools/health.due-date/execute \
  -H 'Content-Type: application/json' \
  -d '{"input":{"method":"last-period","lastPeriod":"2026-01-01","cycleLength":28,"embryo":"day-5","on":"2026-06-01"},"locale":"en"}'

Example answer

{
  "output": {
    "dueDate": "2026-10-08",
    "conceptionDate": "2026-01-15",
    "daysLeft": 129,
    "weeks": 21,
    "days": 4,
    "trimester": 2,
    "pregnancyDays": 151
  },
  "steps": [
    {
      "id": "added",
      "formula": "days added = 280 + (cycle length − 28)",
      "substitution": "days added = 280 + (28 − 28)",
      "value": 280,
      "unit": "days"
    },
    {
      "id": "daysLeft",
      "formula": "days to the due date = due date − day of the calculation",
      "substitution": "days to the due date = 2026-10-08 − 2026-06-01",
      "value": 129,
      "unit": "days"
    },
    {
      "id": "pregnancyDays",
      "formula": "days pregnant = 280 − days to the due date",
      "substitution": "days pregnant = 280 − 129",
      "value": 151,
      "unit": "days"
    },
    {
      "id": "weeks",
      "formula": "weeks of pregnancy = ⌊days pregnant / 7⌋",
      "substitution": "weeks of pregnancy = ⌊151 / 7⌋",
      "value": 21,
      "unit": "weeks"
    },
    {
      "id": "days",
      "formula": "extra days = days pregnant − 7 × weeks of pregnancy",
      "substitution": "extra days = 151 − 7 × 21",
      "value": 4,
      "unit": "days"
    },
    {
      "id": "trimester",
      "formula": "trimester: under 14 weeks 1, under 28 weeks 2, later 3",
      "substitution": "trimester: 21 weeks",
      "value": 2
    }
  ],
  "notes": [],
  "meta": {
    "toolVersion": "1.0.0",
    "locale": "en"
  },
  "citation": {
    "url": "https://hesaplayici.com/en/health/due-date-calculator",
    "title": "Due Date Calculator"
  }
}