Due Date Calculator: Estimate Your Due Date and Weeks Pregnant

Enter the first day of your last period and your usual cycle length. You get an estimated due date, how many weeks pregnant you are today, and when each trimester starts. You can use an English date or a Nepali (BS) date. It runs in your browser, so nothing is sent or stored.

First day of your last period

Calendar

Your estimated due date is

 

    Cycella Pregnancy (free on Google Play) keeps your weeks, visits and questions on your phone. See Cycella Pregnancy.

    Calculated in your browser. Nothing you enter is sent or stored. The due date is an estimate; an ultrasound scan date from your health worker is more accurate.

    Written by the Cycella editorial team. See our editorial policy.

    How the due date calculator works

    A pregnancy is counted as 40 weeks (280 days) from the first day of your last period. That rule assumes a 28-day cycle, with the egg released around day 14. If your cycle is usually longer, the egg is released later, so the due date moves later by the same number of days. If it is shorter, the date moves earlier. The calculator does this for cycles from 21 to 45 days.

    For example, if your last period started on 1 January 2026 and your cycle is 28 days, the estimated due date is 8 October 2026. With a 35-day cycle, it is 15 October 2026.

    How accurate is a due date?

    A due date is a best guess, not an appointment. Only a small share of babies are born on the exact day. Babies born from 37 weeks up to 41 weeks and 6 days are counted as born at term, which is why the calculator shows that window too.

    The date from your last period is less reliable if your cycles are irregular, if you are not sure of the date, or if you became pregnant soon after stopping hormonal birth control or after a pregnancy. In those cases an early ultrasound scan usually gives a better date. If your health worker gives you a different due date, use theirs.

    Weeks and months of pregnancy

    Health workers count pregnancy in weeks because a month is not a fixed length. Roughly, 40 weeks is a little over 9 calendar months. Counting in weeks also makes check-up timing clearer, for example "a check-up at 28 weeks".

    Using a Nepali (BS) date

    Many people in Nepal remember the date of their last period in Bikram Sambat. BS months have 29 to 32 days and change from year to year, so adding "9 months and 7 days" in BS can give the wrong day. The calculator converts your BS date to an English date, counts the days, and converts the answers back. See the Nepali due date calculator, which also shows the check-up timing in Nepal's guideline.

    When to see a health worker

    If you think you are pregnant, contact a doctor, midwife or health worker early, ideally in the first 12 weeks, to start antenatal care. Get help straight away if you have any bleeding from your vagina, severe pain in your belly, a bad headache or blurred vision, fits, fever, swelling of your face or hands, fluid leaking from your vagina, or if your baby moves less than usual later in pregnancy.

    Questions about the due date calculator

    How is the due date worked out?

    The calculator adds 280 days (40 weeks) to the first day of your last period. If your cycle is longer or shorter than 28 days, it moves the date by the difference. This is Naegele's rule, adjusted for cycle length. It is a common way to estimate the date before an ultrasound scan.

    How accurate is the due date?

    It is an estimate. Only a small share of babies arrive on the exact day, and most arrive within a couple of weeks either side. An ultrasound scan early in pregnancy usually gives a more accurate date, so use the date your health worker gives you.

    Why are pregnancy weeks counted from my last period?

    Because the first day of the last period is a date most people know, while the day of conception is usually not known. So in "week 6" of pregnancy, conception happened about 4 weeks earlier.

    Can I enter a Nepali (BS) date?

    Yes. Choose Nepali (BS) and pick the year, month and day. Results are shown in both English and BS dates. BS dates from 2070 to 2090 are supported.

    Is my date stored or sent anywhere?

    No. The calculation runs in your browser. Nothing is sent or stored, and this site has no analytics.

    Keep your weeks, visits and questions in one place. Cycella Pregnancy keeps your weeks, estimated due date, visits, readings and questions on your phone. It is free on Google Play. See Cycella Pregnancy.

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    Sources

    This tool gives estimates from the dates you enter. It is not medical advice. Your health worker's dates always come first. If something worries you, please contact a doctor or health worker.