Pregnancy calculator

Use your last period or your due date to see your weeks and days, your trimester and what is coming next.

Your details

Work it out from
First day of your last period
Usual cycle length
Due date (if you chose due date)

You are

11w 4d

first trimester

  • Due dateSat 8 May 2027
  • Days to go199
  • Coming upFirst midwife appointment (weeks 8 to 12)

Weeks are counted from the first day of your last period, so conception was about 2 weeks into "week 1". Your dating scan may move the date a little; go by the scan once you have it.

Bleeding, tummy pain, a bad headache, blurred vision, fluid leaking or your baby moving less: call your maternity unit or midwife straight away, any time of day. In an emergency call 999.

The working

Counting from your last period

Pregnancy is counted from the first day of your last period, not from conception. If that was 1 August 2026, then on 21 October you are 11 weeks 4 days, in the first trimester, due on 8 May 2027.

Trimesters

How the NHS splits it

TrimesterWeeks
First1 to 12
Second13 to 26
Third27 to birth

Next steps

If you have just found out

  • Refer yourself to maternity services or tell your GP
  • Take folic acid until 12 weeks and vitamin D throughout
  • Cut caffeine to under 200 mg a day
  • Ask about free prescriptions and dental care

Read with care

What this cannot tell you

  • Scan datingOnce you have a dating scan, its date takes over.
  • WellbeingWeeks say nothing about how you or your baby are doing.
  • ConcernsAnything worrying: call your maternity unit.

Questions

Common questions

How do I work out how many weeks pregnant I am?

Count the weeks from the first day of your last period.

When does the second trimester start?

At 13 weeks.

Why am I 4 weeks pregnant if I conceived 2 weeks ago?

Because weeks count from your last period, about 2 weeks before conception.

Sources

Last checked 21 October 2026. Spotted something wrong? Tell us and we will fix it.

Support when you need it

Contact your midwife or GP any time you are worried, and call NHS 111 if you cannot reach them. If a date or a result brings up difficult feelings, Tommy's and the Miscarriage Association offer kind, free support.

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