Due Date Calculator

What is a due date calculator?

A due date calculator estimates the day your baby is due (the estimated due date, or EDD) from the first day of your last menstrual period and your average cycle length. Enter those two values in the tool above and it instantly returns your due date, your estimated conception date, how many weeks and days along you are today, and which trimester you are in.

It answers the first question almost everyone has at the start of pregnancy — “when is my baby due?” — using the same dating method clinics use as a starting point. Because it adjusts for cycle length, it gives a more personal estimate than a fixed 40-week count.

How does the due date calculator work?

It applies Naegele’s rule: it adds 280 days (40 weeks) to the first day of your last menstrual period (LMP). It then adjusts for your cycle by adding cycle − 28 days, because a longer-than-average cycle means you ovulated later, so the due date moves later too. A shorter cycle moves it earlier.

The exact method the widget uses is:

EDD        = LMP + 280 days + (cycle − 28) days
conception = LMP + 14 days  + (cycle − 28) days
how far along = floor((today − LMP) ÷ 1 day) → weeks and days

A few definitions and units:

• LMP — the first day of your last menstrual period, not the day it ended.
• Cycle length — the number of days from the start of one period to the start of the next; 28 days is the default.
• EDD — estimated due date, reported as a calendar date (for example, Sun, 8 Nov 2026).
• Conception — estimated at about 14 days after the LMP (around ovulation), shifted by the same cycle adjustment.
• Trimester — first is under 13 weeks, second is 13 up to 28 weeks, third is 28 weeks onward, measured from the LMP.

So pregnancy is dated from the LMP, which is why the count starts about two weeks before you actually conceived.

Examples

Each example below matches the tool’s output exactly. All three use an LMP of 1 February 2026 so you can see how cycle length alone shifts the result.

Example 1 — average 28-day cycle

• Adjustment: 28 − 28 = 0 days
• EDD: 1 Feb 2026 + 280 days = Sun, 8 Nov 2026
• Conception: 1 Feb 2026 + 14 days = Sun, 15 Feb 2026

Example 2 — longer 32-day cycle

• Adjustment: 32 − 28 = +4 days
• EDD: 1 Feb 2026 + 284 days = Thu, 12 Nov 2026 (4 days later than Example 1)
• Conception: 1 Feb 2026 + 18 days = Thu, 19 Feb 2026

Example 3 — shorter 24-day cycle

• Adjustment: 24 − 28 = −4 days
• EDD: 1 Feb 2026 + 276 days = Wed, 4 Nov 2026 (4 days earlier than Example 1)
• Conception: 1 Feb 2026 + 10 days = Wed, 11 Feb 2026

For the 28-day example, if today were 9 June 2026 you would be 128 days along, which is 18 weeks and 2 days — the second trimester.

Due date by cycle length

This table shows the same LMP of 1 February 2026 across common cycle lengths, straight from the formula above. Notice the EDD shifts exactly one day for each day of cycle length away from 28.

Cycle length	Adjustment	Days added	Estimated due date	Estimated conception
24 days	−4	276	Wed, 4 Nov 2026	Wed, 11 Feb 2026
26 days	−2	278	Fri, 6 Nov 2026	Fri, 13 Feb 2026
28 days	0	280	Sun, 8 Nov 2026	Sun, 15 Feb 2026
30 days	+2	282	Tue, 10 Nov 2026	Tue, 17 Feb 2026
32 days	+4	284	Thu, 12 Nov 2026	Thu, 19 Feb 2026
35 days	+7	287	Sun, 15 Nov 2026	Sun, 22 Feb 2026

Find the row closest to your own cycle, or enter your exact LMP and cycle in the tool above for your personal dates.

What can you use a due date calculator for?

The same estimate supports many early-pregnancy decisions:

• Planning ahead — booking the first scan, antenatal appointments and time off work around an expected date.
• Tracking progress — knowing how many weeks along you are and which trimester you are in.
• Estimating conception — working out roughly when conception happened, which can help with timing questions.
• Counting down — sharing a target month with family or matching it to milestones; for raw day counts between any two dates, the date difference calculator is handy.
• Preparing logistics — scheduling maternity leave, classes and a hospital bag around the due window.

Tips and common mistakes

A few points help you read the result correctly:

• Use the first day of your last period, not the last day, and not the day you think you conceived.
• Set your real cycle length. Leaving it at 28 when your cycle is, say, 33 days will date the pregnancy a few days early.
• Treat the date as a window, not a deadline. Only about 1 in 20 babies arrive on the exact due date; most come within roughly two weeks on either side.
• Irregular cycles reduce accuracy. If your cycles vary a lot, or you do not know your LMP, an early ultrasound gives a better date than any LMP-based formula.
• The count starts before conception. Being “8 weeks pregnant” is measured from the LMP, so the embryo is about two weeks younger than the pregnancy week number.

Limitations and notes

This tool uses a single, widely taught dating rule and cannot account for everything about an individual pregnancy. It assumes ovulation happens about 14 days before the next period and that you know your LMP; for very irregular cycles, an unknown LMP, IVF transfers, or recent hormonal birth control, an LMP-based estimate is less reliable than a clinical dating scan. It does not detect twins, ectopic pregnancy or any complication.

Your inputs stay in your browser. The calculation runs entirely on your device — nothing you type is uploaded or stored, so your dates remain private.

Medical disclaimer: This due date calculator provides a general estimate for information only and is not medical advice. It is not a substitute for an examination, an ultrasound, or professional judgement. For any care decisions, or if you have concerns about your pregnancy, please consult a doctor, midwife or qualified healthcare professional.

For more pregnancy planning, pair this with the ovulation calculator to estimate your fertile window and the pregnancy week calculator to track each week, or browse all related tools on the pregnancy & women page.