Pregnancy Trimester Calculator
Trimester dates, current week and countdown from your last period or due date.
Enter your values
ⓘ Live results
Results
- Current stage
- Second trimester, week 13 day 1
- Estimated due date
- 2026-12-06
- First trimester
- 2026-03-01 to 2026-05-30
- Second trimester
- 2026-05-31 to 2026-09-05
- Third trimester
- 2026-09-06 to 2026-12-05
- Days remaining
- 188 days (26.9 weeks)
- Viability milestone (24 weeks)
- 2026-08-16
Working
- 1due = LMP + 280 days = 2026-12-06
Quick answer
Trimesters split a 40 week pregnancy at weeks 13 and 27, counted from the first day of the last menstrual period rather than conception.
due date = LMP + 280 days
How to use the Pregnancy Trimester Calculator
- 1Enter the first day of your last menstrual period in YYYY-MM-DD format.
- 2Adjust cycle length if yours is not 28 days — the due date shifts by the difference.
- 3Change the date to check to see where you were or will be at any point.
Worked example
Using the values the calculator loads with:
Inputs
- First day of last period2026-03-01
- Cycle length28 days
- Date to check2026-06-01
Results
- Current stageSecond trimester, week 13 day 1
- Estimated due date2026-12-06
- First trimester2026-03-01 to 2026-05-30
- Second trimester2026-05-31 to 2026-09-05
- Third trimester2026-09-06 to 2026-12-05
- Days remaining188 days (26.9 weeks)
- Viability milestone (24 weeks)2026-08-16
- due = LMP + 280 days = 2026-12-06
Frequently asked questions
Why count from the last period and not conception?
Ovulation date is rarely known, but the last period usually is. Clinical dating has used LMP plus 280 days for over a century.
Does an ultrasound date override this?
Yes. A first-trimester scan is more accurate than LMP dating, so use the scan date your clinician gives you if they differ.
About this calculator
- Built and reviewed by James Whitfield · How we build and test calculators
- Report an error
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.