Pregnancy Calculator
Use this pregnancy calculator to estimate key pregnancy dates from the first day of your last period and average cycle length.
Pregnancy dates are estimates. Your clinician may adjust dates after an ultrasound.
How it's calculated
Estimated due date = LMP + 280 days
The standard estimate is 40 weeks from the first day of the last menstrual period. Cycle length can shift the estimate because ovulation timing varies.
What your result means
| Category | Range | What it means |
|---|---|---|
| Conception estimate | About LMP + 14 days | Approximate ovulation and conception timing for a 28-day cycle. |
| Second trimester | Week 14 | A common marker for the start of the second trimester. |
| Third trimester | Week 27 | A common marker for the start of the third trimester. |
| Due date | Week 40 | Estimated date, often adjusted by clinical dating. |
How pregnancy dates are estimated
Pregnancy dating usually starts from the first day of the last menstrual period, even though conception happens later.
Why dates change
Cycle length, ovulation timing, and early ultrasound measurements can all shift the final due date.
Use this as a planning tool
This calculator is useful for planning and understanding milestones, but your clinician's dating should guide medical decisions.
Frequently asked questions
How is a pregnancy due date calculated?
A common estimate is 280 days, or 40 weeks, from the first day of the last menstrual period.
Can cycle length change my due date?
Yes. Longer cycles often mean later ovulation, which can move the estimated due date later.
Is conception exactly two weeks after my period?
Not always. It is a common estimate for a 28-day cycle, but ovulation varies.
Should I rely on this for medical decisions?
No. Use it for planning, and rely on your clinician for pregnancy dating and care.