Completely FREE pregnancy due date calculator. No signup, and completely private. Estimate a due date, the current gestational week, and the trimester from your last menstrual period, a known conception or ovulation date, or an IVF embryo transfer. Nothing you enter leaves your browser.
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How a due date is estimated
The most common method uses Naegele's rule: a full-term pregnancy is counted as 280 days (40 weeks) from the first day of your last menstrual period. That sounds odd — it counts from about two weeks before conception — but it's the clinical standard because the last period is a date most people can identify, whereas the exact moment of conception usually isn't known. If you do know your conception or ovulation date, the tool counts 266 days from there instead, which lands on the same estimate without the two-week assumption.
Cycle length and why it's adjustable
Naegele's rule assumes a 28-day cycle with ovulation on day 14. If your cycles run longer or shorter, ovulation shifts and so does the estimate. When you calculate from your last period, the tool lets you set your average cycle length and adjusts the due date accordingly — a longer cycle pushes the date later, a shorter one pulls it earlier. This small correction makes the estimate more personal than a flat 40-week count.
IVF dating
IVF gives unusually precise dating because the timing is known. For a day-5 blastocyst transfer, the due date is 261 days from transfer; for a day-3 embryo, it's 264 days. Choose the matching method and enter the transfer date. Because the biology is pinned down, IVF estimates are typically the most accurate of the methods offered here.
The estimate is an estimate
This deserves emphasis: a due date is a midpoint, not a deadline. Only about one in twenty babies actually arrives on the estimated date, and a normal term birth can happen across a window of several weeks around it. Your prenatal care provider will confirm or revise the dating with an early ultrasound, which is more accurate than any date-based calculation — especially if your cycles are irregular. Use this tool for planning and orientation, and rely on your provider for the dates that matter medically.
Private by design
A pregnancy is deeply personal information, and this calculator is built so it stays with you: every calculation runs in your browser, nothing you enter is transmitted or stored, and there's no account or sign-up. Unlike many pregnancy sites, there's no email capture and no profile behind the number. For organizing the practical side of a new arrival, the Home Inventory Generator and other document tools live on the same site.
Frequently asked questions
How is my due date calculated from my last period?
It adds 280 days (40 weeks) to the first day of your last menstrual period, adjusted for your average cycle length. That's the standard clinical method, Naegele's rule.
Which method is most accurate?
IVF transfer dates are the most precise because the timing is known exactly. A known conception date is next. The last-period method is a reliable estimate but assumes typical ovulation timing. An early ultrasound from your provider is more accurate than any of them.
Will my baby be born on the due date?
Probably not on the exact day — only about 1 in 20 births lands on the estimated due date. A normal term birth happens across a window of weeks around it. Treat the date as a midpoint, not a deadline.
Important
This is an estimate based on standard averages, not medical advice. Only about 1 in 20 babies is born on the estimated due date. Your prenatal care provider, using an ultrasound, gives the dating you should rely on. Always consult a qualified healthcare professional about your pregnancy.
Support
Problem with this tool or suggestions for improvement? Please email support@niftyutilities.com.