How is 'how many weeks pregnant' calculated?

Pregnancy is counted in weeks from the first day of your last menstrual period, not from conception. This is why you may be told you're 4 weeks pregnant only about 2 weeks after ovulation.

How many trimesters are in pregnancy?

There are three trimesters. The first runs from week 1 to the end of week 12, the second from week 13 through week 27, and the third from week 28 until birth.

Is this calculator accurate?

It gives an accurate arithmetic estimate based on the date you provide. Ultrasound dating in early pregnancy is the most reliable clinical method — always confirm with your care provider.

How many weeks pregnant am I?

Instant answer — enter either your estimated due date or the first day of your last period.

Estimated due date

You are

40 weeks 0 days pregnant

Third trimester

Week 1Week 40

Estimated due date: Sunday, October 4, 2026

This is an estimate for information only — only about 1 in 20 babies arrive on their due date. Always confirm dates with your midwife or doctor.

Related calculators

How many weeks pregnant am I?
Trimester calculator
Pregnancy week by week
Due date calculator

How this page is sourced

SoftBump calculators use the standard dating rules published by national health bodies. Every result is an estimate, and your midwife, obstetrician or fertility team always takes priority over anything shown here.

NHS — You and your baby at 0 to 8 weeks pregnant
ACOG — Methods for estimating the due date

Last reviewed: March 2026