Due Date Calculator
Estimate your baby's due date and see your current gestational week and trimester from your last menstrual period.
Example
If your last menstrual period began on January 1, 2026 with a standard 28-day cycle:
Due date = Jan 1, 2026 + 280 days = Oct 8, 2026
Conception (est.) = Jan 1 + (28 - 14) = Jan 15, 2026
On Mar 1, 2026 (59 days after LMP):
Gestational age = 8w 3d -> First trimester
How it works
Enter the first day of your last menstrual period (LMP); the due date is LMP plus 280 days (Naegele's rule), adjusted for cycle length. The gestational age is the number of completed weeks since the LMP.
Good to know
This Due Date Calculator estimates when a baby is likely to arrive by adding 280 days to the first day of your last menstrual period (LMP), with an adjustment for cycle length. Beyond the estimated due date, it also reports how far along you are right now — your gestational age in weeks and days, the current trimester, an estimated conception date, and a live countdown of days remaining. It's aimed at anyone in early pregnancy or trying to conceive who wants a quick, private snapshot without creating an account.
You'd typically reach for it after a positive test, while you wait for a first prenatal visit, or when you want to sanity-check the date a clinic gave you. Because the math keys off ovulation timing, the cycle-length field matters: leave it at 28 for a standard cycle, or change it if yours is consistently shorter or longer. A longer cycle pushes the due date later and a shorter cycle pulls it earlier, since ovulation (and therefore conception) shifts by roughly the difference from 28 days.
Read the result as a window, not a deadline. The big date is the single most likely point, but births cluster across a range of weeks around it, so the "days remaining" figure is best treated as a rough countdown. The gestational age tells you which trimester you're in: roughly weeks 0–12 are the first trimester, 13–26 the second, and 27 onward the third. If you enter an LMP that is in the future the tool flags it, and past about 42 weeks it will label the pregnancy "post-term."
- Use the exact first day of bleeding for the LMP, not the day spotting started or ended, since the 280-day count begins there.
- An early ultrasound is generally more accurate than LMP-based dating, especially with irregular cycles, so a clinic may revise this estimate — that revision takes precedence.
Frequently asked questions
What is Naegele's rule?
Naegele's rule estimates your due date by adding 280 days (40 weeks) to the first day of your last menstrual period. It assumes a regular 28-day cycle with ovulation around day 14.
How does cycle length change the result?
A standard cycle is 28 days. If yours differs, the due date shifts by the difference: a 32-day cycle adds 4 days, while a 25-day cycle subtracts 3 days, since ovulation timing affects conception.
Is my data uploaded anywhere?
No — this calculator runs entirely in your browser; nothing is uploaded.
Is this a substitute for medical advice?
No. These are educational estimates — consult a qualified health professional for medical decisions.
People also ask
How many weeks pregnant am I based on my last period?
Your gestational age is counted from the first day of your last menstrual period, so it is roughly the number of completed weeks since that date. This calculator shows it as weeks and days (for example, 8w 3d) once you enter your LMP.
Can I calculate a due date if I don't know my last period date?
This tool requires an LMP date to apply Naegele's rule, so without it you cannot get a result here. If you know your conception or ovulation date or have an ultrasound dating, a conception-based or ultrasound estimate is generally used instead.
Why is my due date different from what my doctor told me?
Clinics often date pregnancies using an early ultrasound, which measures the embryo or fetus directly rather than relying on the LMP. Differences also arise from irregular cycles or uncertain period dates, and the ultrasound-based date is usually treated as the more accurate one.
What does gestational age mean versus how old the baby is?
Gestational age is measured from the first day of the last menstrual period, which is about two weeks before conception actually occurs. So gestational age is typically around two weeks greater than the fetus's true age since fertilization.
Is 40 weeks counted from conception or from my last period?
The standard 40-week (280-day) pregnancy length is counted from the first day of the last menstrual period, not from conception. Counted from conception or ovulation, the typical length is closer to 38 weeks.
How accurate is a due date estimate?
A due date is a single most-likely point, and only a small share of births occur exactly on it. Most deliveries happen within a range of about two weeks before to two weeks after the estimated date.
Does an irregular cycle affect the due date calculation?
Yes. Naegele's rule assumes ovulation around day 14 of a 28-day cycle, so irregular or non-28-day cycles can shift the actual conception timing. Adjusting the cycle-length field helps, but ultrasound dating is generally more reliable when cycles are irregular.
How is the estimated conception date worked out?
This tool estimates conception as the LMP plus your cycle length minus 14 days, which approximates the day of ovulation. It is an estimate based on typical timing rather than a confirmed conception date.
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