Pregnancy Calculator
Enter how your pregnancy is dated and the date you want to check. You get the due date, how far along you are, how many days remain and a calendar of milestone dates.
Last updated November 4, 2026
First day of one period to the first day of the next
Result
12 weeks 0 days pregnant on November 12, 2026 (first trimester)
| Measure | Value |
|---|---|
| Estimated due date | Thursday, May 27, 2027 |
| Gestational age | 12 weeks 0 days |
| Trimester | First trimester |
| Days remaining | 196 days |
| Progress | 30% of 280 days |
| Milestone | Date | Status |
|---|---|---|
| Week 4 | September 17, 2026 | Passed |
| Week 8 | October 15, 2026 | Passed |
| Week 12 | November 12, 2026 | Today |
| Second trimester begins | November 26, 2026 | Ahead |
| Week 20 (halfway) | January 7, 2027 | Ahead |
| Third trimester begins | March 4, 2027 | Ahead |
| Week 36 | April 29, 2027 | Ahead |
| Full term begins | May 20, 2027 | Ahead |
| Estimated due date | May 27, 2027 | Ahead |
Trimesters start at weeks 14 and 28. Full term begins at 39 weeks 0 days. These dates are estimates, not a diagnosis or medical advice. Your doctor or midwife sets the due date that counts, often with an ultrasound.
Show the work
Formula: Gestational age = days from the start of the 280-day count (due date - 280) to the as-of date. Progress = days / 280. Milestone = start + 7 x week.
- Last period starts 2026-08-20; average cycle 28 days, so the adjustment is 0 days.
- 2026-08-20 + 280 + (28 - 28) = 2026-08-20 + 280 days = 2027-05-27.
- Start of the 280-day count: 2027-05-27 - 280 days = 2026-08-20.
- Days from 2026-08-20 to 2026-11-12 = 84 = 12 weeks and 0 days (trimester: weeks 0 to 13 first, 14 to 27 second, 28 and up third).
- Days remaining: 280 - 84 = 196. Progress: 84 / 280 = 30%.
- Milestones: 2026-08-20 + 7 x week (week 4 = 2026-09-17, week 40 = 2027-05-27).
Result: 12 weeks 0 days pregnant on November 12, 2026 (first trimester)
How the overview is worked out
gestational age = as-of date − start of count
start = due date − 280 days
progress = days ÷ 280
The calculator first finds a due date from your method (last period, conception, IVF transfer, ultrasound, or a due date you already have). It then counts back 280 days to the start of the pregnancy count and measures the days from there to your as-of date, shown as weeks and days.
Progress is those days divided by 280, capped at 100% from the due date. Days remaining is 280 minus the days counted.
Milestone dates are the start of the count plus 7 days times the week number. Trimesters begin at weeks 14 and 28, and full term begins at 39 weeks 0 days, following the definitions in ACOG Committee Opinions 700 and 579.
See how we calculate for the formulas, sources and review schedule behind every calculator.
This is an estimate, not medical advice
The dates on this page are estimates. Cycle length and pregnancy length vary from person to person and from month to month, so real dates can differ by days or weeks. The tool cannot confirm a pregnancy, ovulation or fertility, is not a method of birth control, and does not replace care from a doctor or midwife. This page has not been reviewed by a medical professional.
Dates the calculator rejects
A last period, conception or scan date later than the as-of date is rejected, and so is an as-of date before the start of the count. Gestational age is limited to 0 to 42 weeks: a date more than 42 weeks after the start usually means a typing mistake, so no result is shown.
Sources
Official and primary sources for the statements on this page. Their authors have not reviewed or endorsed this page.
- NICHD (National Institutes of Health), About Pregnancy (web page, checked November 2, 2026). States that pregnancy usually lasts about 40 weeks, measured from the last menstrual period to delivery
- American College of Obstetricians and Gynecologists, Committee Opinion No. 700: Methods for Estimating the Due Date, Obstetrics & Gynecology 2017;129(5):e150-e154. Says the due date should be set once the last menstrual period, an early ultrasound, or both are available, and that for research and surveillance the best obstetric estimate should be used rather than the last menstrual period alone. By convention the due date is 280 days after the first day of the last period, and an IVF due date uses the embryo age and transfer date (261 days after a day-5 embryo, 263 after a day-3 embryo). It also gives the second trimester as 14 0/7 to 27 6/7 weeks and the third 28 0/7 weeks and beyond. These calculators do not apply its ultrasound redating rules, so their dates are estimates and not clinical dating
- American College of Obstetricians and Gynecologists, Committee Opinion No. 579: Definition of Term Pregnancy, Obstetrics & Gynecology 2013;122(5):1139-1140. Defines early term as 37 0/7 through 38 6/7 weeks, full term as 39 0/7 through 40 6/7 weeks, late term as 41 0/7 through 41 6/7 weeks and postterm as 42 0/7 weeks and beyond
Trimester boundaries match ACOG Committee Opinion 700 (checked November 4, 2026), which calls the first trimester up to and including 13 6/7 weeks, the second trimester 14 0/7 to 27 6/7 weeks and the third trimester 28 0/7 weeks and beyond. NICHD labels them weeks 1 to 12, 13 to 28 and 29 to 40, so other sources draw the lines slightly differently.
The full-term start (39 weeks 0 days) and the other term stages match ACOG Committee Opinion 579 (checked November 4, 2026). The milestone weeks (4, 8, 12, 20, 28, 36, 40) are simple multiples of 7 days from the start of the count, not clinical events.
The IVF offsets (261 days for a day-5 embryo, 263 for a day-3 embryo) and the 280-day count are stated in ACOG Committee Opinion 700. The cycle-length adjustment and the 266-day conception count are conventions that are not stated in the cited sources; 266 is 280 minus 14, from ACOG’s assumption of ovulation on day 14.
How to use the Pregnancy Calculator
- Choose your dating method and enter its date and details.
- Set the as-of date, which is today unless you are looking at another day.
- Read the due date, weeks and days, trimester, days remaining and progress.
- Use the milestone table, then Copy, Print or Share the result.
Worked example
Last period on January 1, 2026, checked on March 1, 2026: 59 days, which is 8 weeks 3 days, first trimester, 221 days to the October 8 due date and 21.1% of 280 days.
| Milestone | Date |
|---|---|
| Week 4 | January 29, 2026 |
| Week 8 | February 26, 2026 |
| Week 12 | March 26, 2026 |
| Second trimester begins (week 14) | April 9, 2026 |
| Week 20 | May 21, 2026 |
| Third trimester begins (week 28) | July 16, 2026 |
| Week 36 | September 10, 2026 |
| Full term begins (week 39) | October 1, 2026 |
| Estimated due date (week 40) | October 8, 2026 |
Frequently asked questions
What does the as-of date do?
It is the day the weeks, trimester and days remaining are measured on, so you can look at today, a past date or a future date.
Why is progress shown as a percentage of 280 days?
Pregnancy is counted as 280 days, so 140 days is 50%. The figure stops at 100% on the due date.
What happens if I am past my due date?
Days remaining shows how many days past the due date you are, up to 42 weeks. Beyond that the calculator shows an error instead of a result.
Do the milestones predict specific events?
No. They are calendar dates at set weeks of the count, not appointment or development schedules.
Are my numbers stored or sent anywhere?
No. The calculation runs in your browser and nothing you enter is saved or uploaded.