Due date calculator
Due date calculator
Enter the first day of your last period to estimate your due date, how far along you are and your trimester.
Updated
Your estimate
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This is an estimate, not a diagnosis or birth control.
How is a due date calculated?
A due date is usually estimated by adding 280 days, or 40 weeks, to the first day of your last period. If your cycles are longer or shorter than 28 days, the date moves by the difference. Only about 1 in 20 babies arrive on their due date, and an early ultrasound may give a more accurate date.
How it's calculated
- Due date = first day of last period + 280 days.
- If your cycle isn't 28 days, the difference is added or taken away. A 35-day cycle moves the date 7 days later.
- Weeks pregnant are counted from the first day of your last period, so you're about 2 weeks pregnant at conception.
- Your doctor or midwife may change the date after a dating ultrasound.
Gyne learns your real cycle and adjusts these estimates as you log.
Frequently asked questions
How accurate is a due date calculator?
It gives a good estimate, but most babies are born within two weeks either side of the date. A dating ultrasound in the first trimester is usually more accurate.
Why are weeks counted from my last period?
Because the date of your last period is easier to know than the day you conceived. Counting this way is the standard doctors use.
What if I don't know the date of my last period?
Your doctor can estimate your due date with an ultrasound. Use your best guess here only as a rough idea.
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