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Due Date Calculator

Estimate a pregnancy due date from the last period and cycle length, with the current week, trimester, and milestone dates.

Calculated in your browser. Nothing is uploaded.

Defaults to 28 days. Adjust it to shift the due date.

Enter the first day of your last period to estimate the due date.

How to calculate a pregnancy due date

  1. Enter your last period

    Pick the first day of your last menstrual period. The estimate appears as soon as the date is valid; there is no button to press.

  2. Set your cycle length

    The cycle length defaults to 28 days. Change it to your own average to shift the due date and conception estimate.

  3. Read the estimate

    See the estimated due date, how far along you are in weeks and days, the current trimester, and a timeline of milestone dates.

  4. Copy the summary

    Click Copy due date summary to place the due date, gestational age, and countdown on your clipboard.

Why use this tool

Due date with cycle correction

The estimate counts 40 weeks from the first day of your last period and shifts the date when your cycle is longer or shorter than 28 days.

How far along, to the day

A live readout shows your current gestational age in weeks and days, the trimester, and a progress bar toward the due date.

Milestone timeline

Dated markers cover the second and third trimesters, the viability point, full term, the due date, and post-term, with each passed milestone checked off.

Estimated conception date

The tool estimates when conception likely occurred from your cycle length, useful for pairing with a dating scan.

Nothing is transmitted

Your dates are processed by the page alone; they are never uploaded, stored, or logged.

About this tool

This due date calculator turns the first day of your last menstrual period into an estimated due date, updating the moment the date is valid. It follows the standard 40-week rule, counting 280 days from the start of your last period, and adjusts that date when your cycle differs from the textbook 28 days, since a longer or shorter cycle moves ovulation and therefore conception.

Below the due date you get a full picture of where the pregnancy stands: the current gestational age in weeks and days, the trimester, a countdown of days to go, and a progress bar. A dated timeline marks the standard milestones, when the second and third trimesters begin, the viability point around 24 weeks, when full term starts at 37 weeks, the due date at 40 weeks, and post-term at 42 weeks, checking off each one you have already passed. An estimated conception date is derived from your cycle length as well.

Every figure is worked out in the page itself, so the dates you enter are never transmitted. Remember that a due date is only an estimate: most babies arrive in the weeks around it, and an early scan can revise the date. To measure a plain gap between two dates instead, use the date difference tool, count how old someone is with the age calculator, or set a reminder for the big day with the countdown timer.

Frequently asked questions

How is the due date calculated?
It counts 40 weeks (280 days) from the first day of your last menstrual period, the same method a clinician uses. When your cycle length is not 28 days, the date is adjusted so it reflects when ovulation and conception most likely happened.
Why does cycle length change the due date?
The 40-week rule assumes a 28-day cycle with ovulation around day 14. If your cycle is longer or shorter, you ovulate later or earlier, so conception and the due date shift by the same number of days.
What is gestational age and how is it counted?
Gestational age is how far along the pregnancy is, measured from the first day of your last period rather than from conception. This tool shows it in weeks and days and uses it to work out the current trimester.
How accurate is the estimate?
It is a well-established estimate, not a guarantee. Only about 1 in 20 babies arrive on the exact due date, and an early ultrasound can revise the date. Treat the result as a guide and confirm it with your care provider.
Is my data uploaded anywhere?
No. Everything runs in your browser; the dates you enter are never sent to a server, stored, or logged.

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