Estimate only. Not medical advice, not for contraception.
Upcoming cycles
Estimates only, not medical advice. Do not use this calculator for contraception. Your midwife or doctor will confirm dates, usually by ultrasound.
For IVF the transfer date and embryo age are known, so the due date is calculated from them instead of a period: 263 days after a day-3 transfer and 261 days after a day-5 (blastocyst) transfer. Both land on the same date as a natural 280-day count from an equivalent last period. Your clinic will confirm the date at the first scan.
How to use
- Choose what you know: the first day of your last period, the conception date, or the IVF transfer date and embryo age.
- For the last period, set your usual cycle length. A cycle longer or shorter than 28 days moves the due date by the same number of days.
- Read your due date, how far along you are today and your trimester. Key dates are listed below; tap any row to copy it.
- Switch to Ovulation to see your fertile window, ovulation day and next period, with a calendar for the coming months.
- Nothing is saved unless you turn on Remember on this device.
- This is an estimate, not medical advice, and it must not be used for contraception. Ovulation varies from cycle to cycle, and only about 4% of babies are born on their due date. Your midwife or doctor will confirm the dates, usually with an early ultrasound.
- Due date from the last period uses Naegele’s rule (first day of the last period + 280 days), adjusted by your cycle length minus 28 days. From conception it adds 266 days; for IVF it adds 263 days after a day-3 transfer or 261 days after a day-5 transfer.
- Pregnancy weeks are counted from the first day of the last period, so “week 6” is about 4 weeks after conception.
- Ovulation is estimated as the next period minus the luteal phase (usually 12–14 days). The fertile window is the 5 days before ovulation plus the day of ovulation and the day after.
- Milestone timings are typical schedules and differ between countries and clinics.
Three ways to calculate
From the last period: Naegele’s rule adds 280 days (40 weeks), then moves the date by your cycle length minus 28 days. A period starting on January 1, 2027 with a 28-day cycle gives October 8, 2027; with a 32-day cycle it becomes October 12.
From conception: add 266 days (38 weeks). From IVF: add 263 days after a day-3 transfer or 261 days after a day-5 blastocyst transfer.
What the date means
The due date marks 40 weeks 0 days, the middle of the normal range rather than a deadline. Most babies are born between 37 and 42 weeks, and only about 4% arrive on the day itself. An early ultrasound often refines the date, and your care team will use that date from then on.
Results are estimates for information, not medical advice, and must not be used for contraception. Your midwife or doctor will confirm dates, usually with an early ultrasound. Nothing is saved unless you turn on Remember on this device.
Frequently asked questions
When is my baby due?
Enter the first day of your last period and your usual cycle length. The estimated due date is about 280 days later for a 28-day cycle.
How do I calculate my due date from conception?
Add 266 days, or 38 weeks, to the conception date. The calculator also shows the matching gestational age.
How is an IVF due date calculated?
Add 263 days to a day-3 transfer date or 261 days to a day-5 transfer date. Both match a standard 280-day count.
Does a longer cycle change the due date?
Yes. Each day your cycle is longer than 28 days moves the due date one day later; a shorter cycle moves it earlier.
Can the due date change?
Yes. If an early ultrasound measures the baby differently from your dates, your midwife or doctor may set a new due date.