Pregnancy Week Calculator
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Gestational age in weeks and days — calculate from last period or from a known due date.
Rates last reviewed: July 2026
Dating method
Gestational age
21 weeks, 5 days
Second trimester (weeks 14–27)
- Total days
- 152
- Trimester (estimate)
- Second trimester (weeks 14–27)
Related calculators
Gestational age in weeks
Gestational age counts from the first day of the last menstrual period (LMP), not from conception. Clinical care uses weeks + days (e.g., “8 weeks 3 days”). Pregnancy is typically dated as 40 weeks from LMP.
If you know your due date instead of LMP, gestational age can be derived: days pregnant = 280 − days until due date. Irregular cycles and IVF pregnancies need clinician-confirmed dating.
Example: LMP March 1, 2026, as of July 31, 2026 → about 21 weeks 5 days pregnant (first trimester complete). Switch to EDD mode if your provider gave you a due date of December 6, 2026 instead.
Official sources
Rates and formulas in this calculator are based on the documentation below. Platforms change fees — confirm current numbers before pricing or payouts.
Common questions
LMP vs ultrasound dating — which wins?
First-trimester ultrasound is often more accurate when LMP is uncertain. This calculator does not replace ultrasound dating.
Why two input modes?
Some people track from their last period; others only know the due date from an early scan. Pick the mode that matches the information you have.
Which trimester am I in?
First trimester runs through week 13, second trimester weeks 14–27, and third trimester from week 28 until delivery. This calculator shows your trimester from completed gestational weeks.