Due Date Calculator API Reference

Overview

Includes pregnancy milestones, percentage completion, and important dates like trimester transitions, perfect for pregnancy tracking and prenatal care applications.

Endpoint

One host, one path per API. The block below shows this call in four languages; every one of them is the same HTTP request. Making requests covers the timeouts, retries and parameter rules that apply to all of them. The SDKs wrap the same call in a typed client.

GEThttps://api.apiverve.com/v1/duedatecalculator

curl "https://api.apiverve.com/v1/duedatecalculator?last_period=2025-06-01" \
  -H "x-api-key: your_api_key_here"

const res = await fetch('https://api.apiverve.com/v1/duedatecalculator?last_period=2025-06-01', {
  headers: { 'x-api-key': 'your_api_key_here' },
});

if (!res.ok) throw new Error(`${res.status} ${await res.text()}`);

const { data } = await res.json();
console.log(data);

import requests

res = requests.get(
    "https://api.apiverve.com/v1/duedatecalculator?last_period=2025-06-01",
    headers={"x-api-key": "your_api_key_here"},
    timeout=15,
)
res.raise_for_status()

print(res.json()["data"])

package main

import (
	"fmt"
	"io"
	"net/http"
)

func main() {
	req, _ := http.NewRequest("GET", "https://api.apiverve.com/v1/duedatecalculator?last_period=2025-06-01", nil)
	req.Header.Set("x-api-key", "your_api_key_here")

	res, err := http.DefaultClient.Do(req)
	if err != nil {
		panic(err)
	}
	defer res.Body.Close()

	out, _ := io.ReadAll(res.Body)
	fmt.Println(string(out))
}

Replace your_api_key_here with the key from your dashboard. When the inputs arrive as a list rather than one at a time, batch requests run up to 200 of them through this same API in a single call.

Authentication

Send your key in the x-api-key header. That is the only auth step — there is no token exchange and no per-endpoint scope to configure. Authentication covers creating, rotating and revoking keys.

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.

Parameters

Sent in the query string. Premium parameters are accepted on every plan but only take effect on plans that include them.

Parameter	Type	Description
`last_period`Required	string	First day of last menstrual period (YYYY-MM-DD) date

Response

Every API returns the same three top-level keys, so one response handler covers your whole integration: status, error and data. Only data changes shape. Response format covers the envelope, the other output formats and how premium fields are withheld.

Sample response

{
  "status": "ok",
  "error": null,
  "data": {
    "calculation_method": "last_period",
    "last_period_date": "2024-01-01",
    "estimated_conception_date": "2024-01-15",
    "due_date": "2024-10-07",
    "current_progress": {
      "days_pregnant": 715,
      "weeks_pregnant": 102,
      "days_into_week": 1,
      "formatted": "102 weeks, 1 days",
      "trimester": 3,
      "percentage_complete": 255.36
    },
    "time_until_due": {
      "days": 0,
      "weeks": 0,
      "days_extra": 0,
      "formatted": "Past due date",
      "is_overdue": true
    },
    "upcoming_milestones": [],
    "important_dates": {
      "end_first_trimester": "2024-04-01",
      "end_second_trimester": "2024-07-08",
      "full_term_begins": "2024-09-16"
    },
    "disclaimer": "This is an estimate only. Due dates can vary. Consult your 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
`calculation_method`	string	`"last_period"`	Method used for calculation: last_period or conception_date
`last_period_date`Premium	string	`"2024-01-01"`	Estimated first day of last menstrual period
`estimated_conception_date`Premium	string	`"2024-01-15"`	Conception date provided as input
`due_date`	string	`"2024-10-07"`	Estimated delivery date in ISO format
`current_progress`	object	`{...}`	How far along the pregnancy is today, in days and weeks
`days_pregnant`Premium	number	`715`	Total number of days pregnant
`weeks_pregnant`Premium	number	`102`	Number of complete weeks of pregnancy
`days_into_week`Premium	number	`1`	Additional days beyond complete weeks
`formatted`Premium	string	`"102 weeks, 1 days"`	Human-readable pregnancy duration with weeks and days
`trimester`Premium	number	`3`	Current trimester number: 1, 2, or 3
`percentage_complete`Premium	number	`255.36`	Pregnancy completion percentage relative to due date
`time_until_due`	object	`{...}`	How long until the due date, with a formatted summary
`days`Premium	number	`0`	Complete days remaining until due date
`weeks`Premium	number	`0`	Complete weeks remaining until due date
`days_extra`Premium	number	`0`	Additional days beyond complete weeks remaining
`formatted`Premium	string	`"Past due date"`	Human-readable time remaining until delivery
`is_overdue`Premium	boolean	`true`	Whether pregnancy has passed the due date
`upcoming_milestones`Premium	array	`[]`	Array of upcoming pregnancy milestones and dates
`important_dates`	object	`{...}`	Key milestones: the end of each trimester and viability
`end_first_trimester`Premium	string	`"2024-04-01"`	Estimated end date of first trimester
`end_second_trimester`Premium	string	`"2024-07-08"`	Estimated end date of second trimester
`full_term_begins`Premium	string	`"2024-09-16"`	Date when pregnancy reaches full term status
`disclaimer`	string	`"This is an estimate only. Due dates can vary. Consult your healthcare provider for medical advice."`	Medical disclaimer about estimated due dates

Errors

Read the HTTP status first, then error for the specific reason. The body names the parameter that has to change. Error handling covers the full status list and which of them are worth retrying.

Status	Meaning	What to do
`400`	Input was rejected	Read `error`; it names the parameter.
`401`	Key missing or invalid	Check the header name and the key value.
`403`	Key valid, but not permitted	A key restriction or IP allow-list; see key scoping.
`429`	Rate limited, or out of credits	Read `error` to tell them apart; see rate limits.

Use cases

Pregnancy Tracking: Build pregnancy tracking applications with accurate due date calculations based on last menstrual period or conception date
Prenatal Care: Calculate gestational age for prenatal care appointments, monitoring fetal development, and scheduling medical tests
Maternity Planning: Create maternity planning tools with delivery date estimates, trimester breakdowns, and important date tracking
Milestone Tracking: Provide pregnancy milestone information with week-by-week pregnancy timeline and key development stages

Other ways to use Due Date Calculator

Set up Due Date Calculator on APIVerve, or reach the same source a different way. Your APIVerve account and credits work on all of them — one key, one balance.

Give it to an AI agentConnect over MCP and your agent calls it as a native tool — Claude, Cursor, ChatGPT.VerveKit →Reference →

Use it in Google Sheets or ExcelA =VERVE() formula fills a column — no script, no export, recalculates in place.VerveSheets →Reference →

Ground an agent on itA cited, machine-checkable fact your model can't produce on its own.VerveContext →Reference →

Due Date Calculator