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Due date calculator

Estimate your baby's due date (Naegele's rule).

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The Due date calculator turns First day of last period into Estimated due date, Estimated conception, instantly and for free. For instance, with First day of last period = 1985-03-20 it returns Estimated due date = 25/12/1985 and Estimated conception = 03/04/1985.

How to use it

  1. Enter your values: First day of last period.
  2. Read the result instantly: Estimated due date, Estimated conception.

Frequently asked questions

How does the Due date calculator work?

It takes First day of last period and derives Estimated due date and Estimated conception from them. The calculation is live as you type, so the result updates on every change.

Which values does the calculator ask for?

A single value: First day of last period. Nothing else is required — no account, no file upload.

What does a typical calculation look like?

With First day of last period = 1985-03-20, the calculator returns Estimated due date = 25/12/1985 and Estimated conception = 03/04/1985. Those figures come from running this exact tool, so you can reproduce them by entering the same values.

When would I actually use this?

Placing a pregnancy on the calendar: the estimated due date, the current week, and when the usual appointments and screenings fall.

What is the most common mistake?

Reading the due date as a deadline. It is a median: fewer than one birth in twenty happens on it, and a normal term spans several weeks around it.

What is the difference between the Due date calculator and the IVF Due Date Calculator?

This one returns Estimated due date and Estimated conception; the IVF Due Date Calculator returns Result. That is the whole difference — open the one whose figure you need.

Is there a tool for the next step?

Conception date calculator is the closest one after this: Estimate the likely conception date from a due date.

What else is worth having open alongside it?

Next period date calculator and Ovulation calculator — they come up in the same task often enough to be worth a second tab.

Where do the figures come from, and how current are they?

Dating follows Naegele's rule (280 days from the last period) or the transfer date for assisted conception. An early ultrasound is more accurate than any calculation and takes precedence over it.

Further reading

All guides →
How-toHow to Calculate Your Due DateNaegele's rule adds 280 days to your last period — or subtract three months and add seven days. Here's how it works and why it's only an estimate.ExplainerOvulation and Your Fertile WindowOvulation is usually 14 days before your next period, and the fertile window spans about six days. Here's how it works and how to estimate yours.ExplainerPregnancy: Weeks to MonthsPregnancy is counted in weeks, but months aren't exactly four weeks. Here's why it's 40 weeks, how weeks map to months and trimesters, and a quick reference.GuidePregnancy Week by Week: The Calendar and What Each Stage MeansPregnancy is counted in 40 weeks from your last period, not from conception — so you are already two weeks pregnant at conception. Here is the full calendar, the trimester boundaries and what term actually means.ExplainerIVF Dating Is the One Case Where the Date Is Actually KnownEvery other pregnancy is dated from an estimate. After IVF, fertilisation is timed to the hour, so gestational age is arithmetic: 266 days from fertilisation, minus the embryo's age at transfer. Here is the derivation for day-3, day-5 and day-6 embryos, why frozen and fresh transfers use the same rule, why an early scan rarely moves an IVF date, and what the two-week offset on a scan report means.ExplainerWhat Is a Normal Menstrual Cycle Length? The Numbers, by Life StageFIGO puts a normal cycle at 24 to 38 days; ACOG's older range is 21 to 35. Here is why two respected bodies give different numbers, how much variation is normal, and how cycles change after menarche and before menopause.