Pregnancy Calculator
Enter the first day of your last period or your conception date to estimate your due date, see how far along you are today, and view your trimester milestones.
Your calculation is performed in your browser.This result is an estimate for informational and educational purposes. It isn’t a diagnosis and isn’t a substitute for advice from a doctor, registered dietitian, or other qualified professional. See our methodology and sources for the formula used and its limitations.
How it works
Pregnancy is dated from the first day of your last menstrual period (LMP), and a full-length pregnancy is counted as 40 weeks (280 days). The calculator adds 280 days to your LMP, adjusting for your cycle length if it is not 28 days. If you know your conception date instead, it adds 266 days, since conception happens roughly two weeks after the LMP.
Formula & methodology
The calculator uses Naegele’s rule, the standard method for estimating a due date. A 40-week pregnancy is 280 days from the first day of the last period, assuming a 28-day cycle and ovulation around day 14. For longer or shorter cycles, the due date shifts by the difference from 28 days. Your current gestational age is then measured from the date that corresponds to a 40-week timeline ending on your due date, so every milestone stays consistent.
Due date = LMP + 280 days + (cycle length − 28)Due date = Conception date + 266 daysConception ≈ LMP + (cycle length − 14) daysGestational age = Today − (Due date − 280 days)What each term means
- LMP
- The first day of your last menstrual period.
- Cycle length
- Days from the first day of one period to the first day of the next. Defaults to 28.
- Gestational age
- Weeks and days of pregnancy, counted from the start of the 40-week timeline rather than from conception.
Trimesters by gestational age
| Trimester | Weeks |
|---|---|
| First | 0 weeks 0 days – 13 weeks 6 days |
| Second | 14 weeks 0 days – 27 weeks 6 days |
| Third | 28 weeks 0 days – birth |
Worked example
If the first day of your last period was January 1, 2026 and your cycle is 28 days, your estimated due date is Thursday, October 8, 2026. Conception is estimated around January 15, 2026, the second trimester begins on April 9, 2026 (week 14), and the third trimester begins on July 16, 2026 (week 28).
Common uses
- —Getting a first estimate of your due date after a positive pregnancy test.
- —Finding out how many weeks and days pregnant you are today.
- —Planning ahead for appointments, leave from work, and trimester milestones.
- —Estimating when conception likely occurred.
Important notes
- —A due date is an estimate. Only a small share of babies are born on their exact due date, and most arrive within a few weeks either side of it.
- —Gestational age is counted from your last period, so you are considered about two weeks pregnant at the moment of conception.
- —If an early ultrasound gives a different due date than your LMP, your doctor or midwife will usually go with the ultrasound date. Always follow the dating your care provider gives you.
- —This calculator is not intended for pregnancies conceived with IVF. Your fertility clinic will provide a due date based on your embryo transfer date.