MamaSkin

A little help from MamaSkin

Pregnancy due date calculator

Find your estimated due date from your last period and usual cycle length.

Start with your dates

Use the day your period started.

From the start of one period to the next. Change 28 to your usual cycle length.

For regular cycles of 21–35 days. If your cycles vary, you’re unsure of your dates, or you had IVF, use the due date from your care team in our pregnancy weeks calculator.

No signup needed. We don’t send or save the dates you enter.

Your estimate will appear here

A few dates, and a little more clarity about the weeks ahead.

A date, with a little context

This is a period-based estimate for regular cycles. It starts with a 40-week pregnancy and adjusts for your usual cycle length.

A scan or your care team may give you different dates. Their agreed dating should guide your care.

How we calculate it

Due date = first day of last period + 280 days + (usual cycle length − 28 days).

Pregnancy days on a chosen date = 280 − the number of days from that date to the due date. We divide by 7 to show completed weeks and the remaining days.

Cycle adjustment is a rough assumption about ovulation timing. It cannot establish when you ovulated or conceived. The tool supports estimates from 0 to 42 weeks and has a separate IVF calculator for embryo-transfer dating.

Sources & a note from us

We’ve used established pregnancy-dating conventions. These sources explain the approach; they haven’t reviewed or endorsed this calculator.

Sources checked 27 October 2026. General information, not a diagnosis or personal medical advice. This calculator cannot confirm pregnancy.

A worked example

For an example period starting on 4 August 2026 with a 28-day cycle, the estimated due date is 11 May 2027. Changing the cycle to 30 days moves the estimate to 13 May 2027.

Example dates only. Your own result uses the dates you enter.

Your questions, answered

How is my due date calculated?

The estimate starts 280 days, or 40 weeks, after the first day of your last period. For a regular cycle, we add or subtract the difference from 28 days. A 30-day cycle adds two days; a 26-day cycle subtracts two.

What if my periods are irregular or I had IVF?

A period-based estimate may not fit your situation. Use the date agreed with your midwife or fertility clinic. You can enter that date in our pregnancy weeks calculator.

Can a dating scan change my due date?

Yes. Early ultrasound can give a more accurate estimate than a period date alone. Follow the due date your care team has agreed, even if a calculator gives a different answer.

Will my baby arrive on this date?

A due date is a reference point, not a promised birthday. The calculator cannot predict when labour will begin or replace your maternity appointments.

A skincare question, too?

If you’re wondering about a bottle on your shelf, our ingredient checker is a good place to start.

Check my ingredients