Pregnancy planner

Due date calculator

Work out your due date from your last period, a scan, your conception date or IVF. See instantly how many weeks pregnant you are and what's coming.

  • Follows official dating rules
  • Calculated on your device
  • Done in 30 seconds

Your details

Not sure? Leave "28 days (average)" as it is.
Shown on your report as e.g. "10+3": enter 10 and 3.
Your details never leave your device and are not stored.
Your due date
Fewer than 5 in 100 babies arrive exactly on this date. Think of it as the heart of your birth window (weeks 37-42).
40 wks
Birth window (37-42 wks)
Trimester
To go

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What does this date mean?

A pregnancy lasts 40 weeks on average, counted from the first day of your last period, so your due date is an average. Most babies arrive somewhere between week 37 and week 42, and all of that is right on time.

Having a dating scan soon? That's where the date is set definitively. Scan dating is more precise than any calculation beforehand and applies from that moment on.

SOURCES1. NHS: Pregnancy due date  ·  2. ACOG: Methods for estimating the due date  ·  3. NVOG/KNOV: Datering van de zwangerschap
This result is a guide. It never replaces assessment by your midwife or doctor. After your dating scan, the scan's dating applies.

How the due date calculator works

The calculation adds 280 days (40 weeks) to the first day of your last period, plus a correction for your cycle length. With a 30-day cycle your date shifts by 2 days. Know your conception date? Then it counts 266 days. Midwives calculate the same way until the dating scan fixes the date.

The result is an estimated due date: the moment you are 40 weeks pregnant. It's the starting point for all your appointments and your maternity leave.

How many weeks pregnant am I?

Pregnancy weeks count from the first day of your last period, not from conception. That's why you're usually already 4 to 5 weeks pregnant when the test turns positive. The calculator shows your exact position in weeks plus days, and which trimester you're in.

Due date after a scan, conception or IVF

Already had a scan, or pregnant through IVF? Then the calculator uses that, because those details are more precise than your period. For IVF it counts from the transfer date plus the embryo age. For a scan, from the gestational age on the report. Most online calculators only work with your period; this one works with all four.

How accurate is a due date?

Treat the date as the middle of a window, because fewer than 5 in 100 babies arrive exactly on it. From week 37 your baby is full term and it can happen any moment. Past 42 weeks, your midwife or doctor will discuss the options with you.

Frequently asked questions

How does a due date calculator work?
It adds 280 days to the first day of your last period, corrected for your cycle length. Or it counts 266 days from conception. Enter your details above and you'll see your date instantly.
How many weeks pregnant am I?
Weeks count from the first day of your last period. The calculator shows it precisely in weeks plus days. At a positive test you're usually already 4 to 5 weeks along.
Is it better to calculate from conception or the last period?
If you know your exact conception date, that's slightly more precise (266 days). Most women know their last period better, which is why that's the standard method worldwide.
What about IVF?
Choose the IVF option and enter your transfer date plus the embryo age (day 3, 5 or 6). Because the transfer moment is known exactly, this is the most precise calculation there is.
Can my due date change?
Yes. At your dating scan (around 10-13 weeks) the date is set definitively, and that dating applies from then on. It can differ a few days from your calculation.
What is an estimated due date?
The day you are 40 weeks pregnant. It's an average, and it marks the heart of your birth window: most babies arrive between week 37 and week 42.
What if I don't know my last period?
Use the scan option: enter the scan date plus the gestational age on the report (for example 10+3). That's even more precise than calculating from your period.
How accurate is a due date calculator?
It follows the same rules midwives use before the first scan. Fewer than 5 in 100 babies arrive exactly on the date, so treat it as the middle of your birth window rather than a deadline.
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