Pregnancy Trimester Calculator
Your trimester, its start and end dates, and days left. Free, private and instant.
How to use the Trimester Calculator
- Choose work out from my: Last period date or Due date.
- Answer any extra questions that appear for your choices.
- Press Calculate to get an instant result with a colour scale, chart and plain-English explanation.
About the Trimester Calculator
Pregnancy is divided into three trimesters. Enter your last period or due date to see which trimester you are in, the date range of each trimester, days left in the current one and your overall progress.
Also known as: trimester calculator, which trimester am I in, pregnancy trimester dates, second trimester start date.
Worked example
Dates in this example are worked out as if today were 5 Nov 2026.
- Work out from my: Last period date
- First day of your last period: 18 Jul 2026
You are in your: 2nd trimester (15 weeks 5 days ยท 86 days left in this trimester). You are 15 weeks 5 days pregnant, in your second trimester. It started on 24 Oct 2026 and ends around 29 Jan 2027.
- First trimester: 18 Jul - 23 Oct 2026
- Second trimester: 24 Oct - 29 Jan 2027
- Third trimester: 30 Jan - 24 Apr 2027
- Days into this trimester: 12
Formula and cut-offs
First trimester: weeks 1-13 (to 13 weeks 6 days). Second trimester: weeks 14-27. Third trimester: weeks 28-40. Dates = last period + 7 x week number.
Frequently asked questions
When does the second trimester start?
At 14 weeks, which is 13 weeks and 7 days after the first day of your last period.
When does the third trimester begin?
At 28 weeks.
Which trimester has the highest miscarriage risk?
The first trimester. The risk drops after about 12 weeks.
Sources and references
- ACOG Committee Opinion 700 - Methods for estimating the due date
- Institute of Medicine (2009) - Weight Gain During Pregnancy: Reexamining the Guidelines
- NHS - Pregnancy guide
Written and checked by the MediHub editorial team against the sources above. Read how we build and review our calculators.
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Last updated . This calculator is for education only and is not medical advice. See the medical disclaimer.