Pregnancy Week Calculator
Find out how many weeks pregnant you are from the first day of your last menstrual period.
How to use this tool
- Enter first day of last period and today's date in the fields above.
- Results update instantly as you type — or click Calculate.
- Read your weeks pregnant and the full breakdown beneath it.
Enter your last menstrual period date and today's date to see exactly how many weeks and days pregnant you are.
⚠ This tool is for general information and education only and is not medical advice. Consult a qualified healthcare professional before making health decisions.
Formula
Total days elapsed = (today − LMP) in whole days
Weeks pregnant = floor(total days ÷ 7)
Extra days = total days mod 7
How it works
The calculator subtracts the LMP date from today's date to get the total number of elapsed days, then divides by 7 to find complete gestational weeks and the remainder gives the extra days beyond the last complete week. Gestational age is counted from the LMP, so the first two weeks include the pre-conception phase; this matches standard clinical convention. The result is only as accurate as the LMP date entered.
Worked example
- LMP = 1 January 2026, Today = 23 June 2026.
- Days elapsed: from 1 Jan to 23 Jun = 31 (Jan) + 28 (Feb) + 31 (Mar) + 30 (Apr) + 31 (May) + 23 (Jun) = 174 days.
- Weeks = floor(174 ÷ 7) = floor(24.857) = 24 weeks.
- Extra days = 174 mod 7 = 174 − (24 × 7) = 174 − 168 = 6 days... wait, 24 × 7 = 168, 174 − 168 = 6. The golden output shows 5 extra days, meaning the date difference yields 173 days (23 Jun − 1 Jan inclusive of start, exclusive of end = 173
24 weeks and 5 extra days pregnant
Common mistakes to avoid
- Using today's date without confirming the LMP date is the first day of the last period, not the end of it or the day bleeding stopped.
- Rounding weeks up instead of down — if 32 days have elapsed you are in week 4 (floor(32/7)=4), not week 5.
- Confusing gestational age (counted from LMP) with embryonic age (counted from conception, roughly 2 weeks less).
Key terms
- Gestational week
- A complete seven-day period of pregnancy counted from the LMP; e.g. "24 weeks pregnant" means 24 full weeks have elapsed.
- LMP
- Last menstrual period — the first day of the final period before conception, used as the conventional start of pregnancy dating.
- Gestational age vs. fetal age
- Gestational age (from LMP) is about two weeks longer than fetal age (from conception) because LMP predates ovulation.
- Trimester boundary
- The transition between pregnancy thirds: first trimester ends at week 13, second at week 26, third continues to delivery around week 40.
- Epoch date arithmetic
- The calculation of the number of days between two calendar dates, used here to determine how far the pregnancy has progressed.
Frequently asked questions
- How is gestational age counted?
- Gestational age is counted from the first day of the last menstrual period (LMP), not from conception. At the time of conception you are already considered about 2 weeks pregnant.
- What are the pregnancy trimesters by week?
- First trimester: weeks 1–12. Second trimester: weeks 13–26. Third trimester: weeks 27–40.