Most common method — assumes an average 28-day cycle.
If you know roughly when conception occurred (e.g. from ovulation tracking or IVF).
Your Estimated Due Date
40 weeks from your last period · only ~5% of babies arrive on their exact due date
LMPDue date
Gestational age today—
Current trimester—
Days until due date—
Milestone
Date
Your baby is about the size of
—
How it works
Pick your dating method. Most people use the first day of their last period (LMP); if you know your conception date instead, use that toggle.
Enter the date. That's the only input needed.
We add 280 days. This is the standard "Naegele's rule" estimate — 40 weeks from LMP, or 266 days from conception (accounting for the ~2 weeks before ovulation).
See your progress. Your current gestational age, trimester, and days remaining are calculated from today's date automatically.
Track milestones. Key dates like end of first trimester, viability, and full term are laid out on a timeline, with passed ones marked off.
This is a statistical estimate, not a prediction — only about 5% of babies arrive exactly on their due date. Your OB/midwife's ultrasound-based dating is generally more precise.
Frequently asked questions
This calculator uses Naegele's rule — adding 280 days (40 weeks) to the first day of your last menstrual period — the same standard method used in most clinical settings for an initial estimate.
It's a solid starting estimate, but only about 5% of babies are born exactly on their due date. An ultrasound dating scan, especially in the first trimester, is generally considered more precise.
LMP-based dating (the default) assumes a standard 28-day cycle. If you know your actual conception date instead, that toggle adjusts the math accordingly for a potentially more personalized estimate.
Gestational age is how far along a pregnancy is, counted in weeks and days from the first day of the last menstrual period — not from the actual conception date, which is about 2 weeks later.
The second trimester typically begins around week 14, and the third trimester around week 28 — both are marked on the milestone timeline above.
Yes — after calculating, you'll see a fun size comparison (like "the size of a lime" or "the size of a papaya") based on your current week, using commonly cited average measurements. It's a general guide, not a growth diagnosis.
Yes — your last calculation is saved privately in your browser, so when you return, your gestational age, trimester, and countdown are automatically shown without re-entering your dates.
This is a general estimate based on standard 40-week (280-day) gestation from LMP or 266 days from conception — actual due dates vary and ultrasound dating may differ. This isn't medical advice; your OB/midwife's dating is the most reliable source.