Pregnancy Calculator · Practical guide
How Many Weeks Pregnant Am I?
Count from the first day of your last period, divide by seven, and see your trimester and due date instantly.
At a glance
The Quick Answer
Count the days from the first day of your last menstrual period (LMP) to today, then divide by seven. The whole number is your completed weeks and the remainder is extra days. For example, if your LMP started June 1, 2026 and today is September 6, 2026, that is 97 days — so you are 13 weeks and 6 days pregnant.
Interactive tool
Pregnancy Calculator
Enter your own values, then compare the result with the examples below.
Milestones
| Week | Milestone | Date |
|---|---|---|
| Week 8 | Heartbeat detectable | -- |
| Week 12 | End of first trimester | -- |
| Week 20 | Anatomy scan | -- |
| Week 27 | Start of third trimester | -- |
| Week 40 | Estimated due date | -- |
Why the Count Starts Before Conception
Doctors date pregnancy from the LMP rather than conception because the period date is far easier to pin down. Conception typically happens about two weeks after the LMP, so your gestational age runs roughly two weeks ahead of the time since fertilization. At 13 weeks 6 days, the embryo itself has been developing for about 12 weeks.
Weeks to Trimester Reference
| Trimester | Gestational Age | Days Since LMP |
|---|---|---|
| First | 0 weeks – 12 weeks 6 days | 0–90 |
| Second | 13 weeks – 26 weeks 6 days | 91–188 |
| Third | 27 weeks – delivery | 189–280+ |
If Your Cycle Is Not 28 Days
The standard count assumes ovulation on day 14 of a 28-day cycle. With a consistently longer 35-day cycle, add 7 days to your expected due date; with a shorter 24-day cycle, subtract 4. When cycles are irregular, an early ultrasound is the most reliable way to confirm how far along you are.
Frequently Asked Questions
Is pregnancy counted from conception or my last period?
From the first day of your last menstrual period. Conception usually occurs about two weeks later, so gestational age is roughly two weeks ahead of the time since fertilization.
How many weeks is a full-term pregnancy?
Your due date sits at 40 weeks from the LMP. Only about 5% of babies arrive exactly on that date; a normal full-term delivery can occur anywhere from 37 to 42 weeks.
Why does my app show a different week than my doctor?
Apps and providers can use slightly different trimester conventions, and your doctor may re-date the pregnancy from an early ultrasound if it disagrees with LMP dating by more than about a week.
What if I cannot remember my last period?
Enter the due date your provider gave you instead — the calculator works backward to find your current week. A first-trimester ultrasound can also date the pregnancy to within about five to seven days.