Health
Pregnancy Due Date Calculator
Estimate your due date in seconds. Enter the first day of your last menstrual period (and your cycle length if it isn't 28 days) to see your estimated due date, how many weeks along you are, your trimester, and the likely conception date.
Estimated due date
Sunday, February 14, 2027
You are now
10w 0d
Trimester
First
Estimated conception date
Sunday, May 24, 2026
Days until due date
210
Based on Naegele's rule (LMP + 280 days), adjusted for your cycle length. Only about 5% of babies arrive on their due date — most come within two weeks either side. Your provider may adjust the date after an ultrasound.
How it works
The estimate uses Naegele's rule, the standard method in obstetrics: due date = first day of your last menstrual period (LMP) plus 280 days (40 weeks). Pregnancy is counted from the LMP rather than conception because the LMP is a date most people actually know.
If your cycles aren't 28 days, ovulation — and therefore conception — shifts, so the calculator adjusts the due date by the difference. A 32-day cycle typically means ovulating around day 18 instead of day 14, pushing the due date about 4 days later.
Only about 5% of babies arrive on their due date; most come within a two-week window either side. A first-trimester ultrasound dates the pregnancy more precisely, and providers will update your official due date if it differs meaningfully from the LMP estimate.
Due date = LMP + 280 days + (cycle length − 28)
Conception ≈ LMP + (cycle length − 14)
Weeks along = (today − LMP) / 7
Example: LMP May 10, 28-day cycle → due Feb 14 (LMP + 280 days)Frequently asked questions
How accurate is a due date calculated from my last period?
It's a good estimate but not a promise: only about 5% of babies are born on their due date, and roughly 80% arrive between 38 and 42 weeks. First-trimester ultrasound dating is more accurate and may shift the estimate by a few days.
Why is pregnancy counted from the last period, not conception?
Because the LMP is a known date while conception usually isn't. Counting from the LMP adds about two weeks before conception even occurs — which is why a '6-week' pregnancy is only about 4 weeks after conception.
What if my cycles are irregular?
LMP-based estimates get unreliable with irregular cycles, since ovulation timing is unpredictable. In that case an early dating ultrasound is the way to go — it measures the embryo directly and is accurate to about ±5 days in the first trimester.
When do the trimesters start and end?
Common convention: the first trimester runs through week 13, the second from week 13 to 27, and the third from week 27 to birth. Sources vary by a week — your provider's convention is the one that matters for your care schedule.
Is this calculator medical advice?
No — it's an arithmetic estimate based on standard formulas. Always confirm dates and pregnancy care decisions with your doctor or midwife.