Due Date Calculator
Estimate due date from last periodRuns locally · nothing uploaded
Estimated due date
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Current week
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Trimester
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Days to go
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Estimates based on general formulas, for information only. Not a substitute for professional medical advice, diagnosis or treatment.
The due date and pregnancy week are formula-based estimates, not medical advice. Attend your prenatal checkups and follow your provider's dating; seek care immediately for pain or bleeding.
How it works
When to use it
- Estimate the due date and current gestational age from the last menstrual period (LMP).
- Adjust for cycles longer or shorter than 28 days.
Formula
Due date = first day of LMP + 280 days + (cycle length − 28) daysNaegele's rule expressed in days.
Gestational age = (today − LMP − cycle adjustment) ÷ 7Worked example
Given: LMP January 1, 2026, 28-day cycle
- 2026-01-01 + 280 days = 2026-10-08.
- With a 30-day cycle, add 2 days: 2026-10-10.
Result: Estimated due date: October 8, 2026.
Reading the result
- Only about 4–5% of babies arrive on the due date; birth between 37 and 42 weeks is considered term.
- A first-trimester ultrasound is more accurate. If it differs substantially, your provider will use the ultrasound date.
Limitations
- Less accurate with irregular cycles, uncertain LMP, recent hormonal contraception or IVF.
- For reference only; follow your provider's advice.
Sources
- ACOG Committee Opinion No. 700: Methods for Estimating the Due Date (2017)
How to use
- 1Pick the first day of your last period.
- 2Enter your average cycle length (default 28 days).
- 3Read your due date and current week.
FAQ
How is the due date calculated?
Naegele's rule: first day of the last period + 280 days, adjusted for cycle length.
How accurate is it?
Few babies arrive on the exact date. Your provider may adjust it based on an ultrasound.