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.
How many weeks pregnant am I? Pregnancy weeks are counted from the first day of your last period, not from conception, so at conception you are already about 2 weeks along. Enter that date to see your week and day (for example 12w 3d), your trimester and how many weeks remain until the estimated due date at 40 weeks.
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.
How pregnancy weeks are counted
Pregnancy is dated from the first day of the last menstrual period (LMP), so it lasts about 40 weeks or 280 days even though conception usually happens around week 2. That is why week 6 is roughly 4 weeks after conception. Weeks are written as completed weeks plus days, such as 20w 4d.
The first trimester runs through week 13, the second from week 14 to week 27 and the third from week 28 until birth. Full term is usually defined as 39 weeks 0 days to 40 weeks 6 days.
Why the due date is only an estimate
Naegele’s rule adds 280 days to the LMP and assumes a 28-day cycle; a longer or shorter cycle shifts the date by the difference, which the calculator applies. Only about 4% of babies arrive on the due date itself, and most are born within two weeks either side.
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
How many weeks pregnant am I?
Count from the first day of your last period. If that was 10 weeks and 3 days ago, you are 10w 3d pregnant, even though conception was about 8 weeks ago.
How is the due date calculated?
By Naegele’s rule: the first day of the last period plus 280 days, adjusted by your cycle length minus 28 days. From a known conception date it is conception plus 266 days.
When does each trimester start?
The first trimester covers weeks 1–13, the second weeks 14–27 and the third week 28 until birth. Some countries draw the lines a week differently.
How accurate is the due date?
It is an estimate. Only about 4% of babies are born on it, and an early ultrasound is usually used to confirm or adjust the date.
Can I use it if my cycle is irregular?
You can, but the result is less reliable. With irregular cycles an early ultrasound measurement is the better way to date the pregnancy.