Pregnancy Due Date Calculator
Estimate your pregnancy due date from your last period or conception date, with cycle-length adjustment, current week, and trimester.
A pregnancy due date calculator that estimates when your baby is likely to arrive. Enter the first day of your last menstrual period, or the conception date if you know it, and the tool applies Naegele's rule to project a due date. It adjusts for cycle lengths other than 28 days, then shows how many weeks and days along you are today, your current trimester, and an estimated conception date. Every calculation runs in your browser.
A due date is an estimate of when a full-term pregnancy will reach delivery, roughly 40 weeks after the first day of the last menstrual period. This calculator uses Naegele's rule, the standard clinical method: it counts 280 days forward from the start of your last period. Because that rule assumes a textbook 28-day cycle with ovulation on day 14, the tool lets you enter your own average cycle length and shifts the estimate accordingly. If you instead know the date of conception or ovulation, switching to that mode counts 266 days forward, which removes the cycle-length assumption entirely.
Alongside the due date, the calculator reports your current gestational age in completed weeks and days, the trimester you are in, and an estimated conception date. Gestational age is measured from the last period, not from conception, which is why a person is considered two weeks pregnant before conception actually occurs. Keep in mind that only about 4 percent of babies arrive on their exact predicted date, and a normal term spans from 37 to 42 weeks. An early ultrasound dating scan is more accurate than any date-based formula, so use this result for planning and let your provider confirm the official date.
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Choose your starting point
Pick the Last period tab if you know the first day of your most recent period, or the Conception date tab if you know when ovulation or conception happened.
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Enter the date and cycle length
Select the date with the picker. In last-period mode, set your average cycle length so the estimate adjusts for cycles shorter or longer than 28 days.
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Read your estimate
See your estimated due date, how far along you are in weeks and days, your current trimester, and the estimated conception date.
Plan around your due date
Get a target date to schedule maternity leave, prenatal appointments, and time off well in advance.
Track how far along you are
Check your current week and trimester at any point to follow your pregnancy's progress between appointments.
Adjust for an irregular cycle
Enter a cycle length of 30 or 35 days to get an estimate that fits your body rather than a generic 28-day assumption.
Estimate from a known conception date
Used IVF or tracked ovulation? Switch to conception mode for a date that skips the cycle-length guesswork.
How is the due date calculated?
From your last period, the tool adds 280 days (Naegele's rule) and shifts the result by the difference between your cycle length and 28 days. From a conception date, it adds 266 days. Both produce an estimated 40-week term.
How accurate is a due date?
Only around 4 percent of babies are born on their exact due date, and full term spans 37 to 42 weeks. A first-trimester ultrasound is more precise than a date-based calculation, so treat this number as a planning estimate.
Why am I two weeks pregnant before conception?
Gestational age is counted from the first day of your last period, which is about two weeks before ovulation. That convention is why your week count is ahead of the actual time since conception.
What if my cycle is not 28 days?
Set your real average cycle length in last-period mode. A longer cycle pushes the due date later and a shorter cycle pulls it earlier, because ovulation timing changes with cycle length.
Is my information private?
Yes. The dates you enter are processed entirely in your browser and never sent to a server or stored anywhere outside your device.