Pregnancy Due Date Calculator
Find your due date, current week, trimester, and key milestones. Works from your last period, conception date, or ultrasound. Free, instant, works worldwide.
About This Pregnancy Due Date Calculator
This free pregnancy due date calculator uses the most widely accepted medical method, Naegele’s Rule, to estimate your expected delivery date. Based on a standard 280-day (40-week) pregnancy counted from the first day of your last menstrual period (LMP), it calculates your due date, current week, trimester, and all the key milestones of your pregnancy journey.
You can calculate using three methods: your last period date (most common), your known or estimated conception date, or the gestational age shown on your ultrasound scan report. All three methods use the same underlying calculation, and they simply start from different known points.
The calculator works for pregnancies worldwide. It accounts for cycle length variations when using the LMP method. If your cycle is longer or shorter than the standard 28 days, your ovulation date and conception window shift accordingly, and the calculator adjusts your due date to reflect this.
Remember that due dates are estimates, and only about 5% of babies are born exactly on their due date. Most births occur between 38 and 42 weeks. Always confirm your due date with your healthcare provider, who may adjust it based on your ultrasound measurements.
Frequently Asked Questions
The most common method is Naegele’s Rule: take the first day of your last menstrual period, add 280 days (40 weeks), and that is your estimated due date. For cycles other than 28 days, the calculator adds the difference between your cycle length and 28 days to adjust the ovulation and conception window accordingly.
The first trimester runs from week 1 to the end of week 13. The second trimester covers weeks 14 through 26. The third trimester runs from week 27 through week 40. Each trimester brings different developmental milestones and physical changes for both mother and baby.
This calculator uses the same Naegele’s Rule formula used by most healthcare providers worldwide. However, only about 5% of babies arrive exactly on their due date. Ultrasound measurements in the first trimester, before 14 weeks, are the most accurate way to confirm gestational age. Always discuss your due date with your midwife or doctor.
Gestational age is counted from the first day of your last period, which is the standard medical measurement shown on your scan and used in this calculator. Foetal age, also called fertilisation age, counts from conception, which is approximately two weeks less. When doctors and midwives say you are 12 weeks pregnant, they mean 12 weeks gestational age.
A full-term pregnancy is between 39 weeks 0 days and 40 weeks 6 days. Babies born between 37 and 38 weeks 6 days are considered early term. The WHO and most medical guidelines consider 40 weeks the ideal duration for full foetal development. This calculator marks your 39-week date as the start of the full-term window.
Yes, use the Ultrasound / IVF mode. For a Day 5 transfer, your due date is the transfer date plus 261 days. For a Day 3 transfer, add 263 days. Your fertility clinic will provide a gestational age at your first scan, which you can enter directly into the Ultrasound mode for the most accurate calculation.