Pregnancy Due Date Calculator
Due date from your last period, conception date, IVF transfer or a scan date, with how many weeks pregnant you are today, trimester and key milestone dates.
Pregnancy Due Date Calculator: with the default inputs, estimated due date is June 17, 2027.
The date matching the method above.
- Gestational age today
- 0 weeks, 0 days
- Trimester
- First trimester (weeks 0–13)
- Days until due date
- 280
- Estimated conception date
- September 24, 2026
- Dating LMP (due date − 280 days)
- September 10, 2026The 'week 0' the milestones count from.
Assumptions
- 280 days from LMP (Naegele's rule) with a ±1 day per day adjustment for cycles other than 28 days; 266 days from conception.
- Gestational age is computed against today's date on your device.
- Milestone weeks are typical windows and vary by provider and country. This is not medical advice; your care team's dating takes precedence.
| Week | Date | What happens | |
|---|---|---|---|
| 4 | October 8, 2026 | Missed period; home test turns positive | in 28 days |
| 8 | November 5, 2026 | Typical first prenatal visit and dating scan | in 56 days |
| 12 | December 3, 2026 | Nuchal translucency screen window (11–14 wk); end of first trimester at 13w6d | in 84 days |
| 20 | January 28, 2027 | Anatomy scan window (18–22 wk) | in 140 days |
| 24 | February 25, 2027 | Threshold of viability; glucose screen (24–28 wk) | in 168 days |
| 28 | March 25, 2027 | Third trimester begins; Tdap and Rh immunoglobulin if needed | in 196 days |
| 36 | May 20, 2027 | Group B strep swab (36–37 wk) | in 252 days |
| 37 | May 27, 2027 | Early term | in 259 days |
| 39 | June 10, 2027 | Full term | in 273 days |
| 40 | June 17, 2027 | Estimated due date | in 280 days |
| 42 | July 1, 2027 | Post-term; induction usually offered by 41–42 wk | in 294 days |
Weeks count from the dating LMP (due date − 280 days), the convention used on every scan report.
How this is worked out
The formula
Naegele's rule: due date = first day of last period + 280 days (40 weeks), adjusted by (cycle length − 28) days From conception: due date = conception + 266 days (38 weeks) IVF: due date = transfer date + 266 − embryo age (3 or 5 days) Gestational age today = today − (due date − 280 days)
Open How it’s calculated above to see this worked through with your own numbers.
What you enter
- Calculate from
- Choose one of 5 options.First day of last menstrual period · Conception / ovulation date · IVF — day-3 embryo transfer · IVF — day-5 (blastocyst) transfer · Known due date (from a scan)
- Date
- The date matching the method above.defaults to today
- Average cycle length(under More options)
- Used only with the last-period method. Naegele's rule assumes 28; longer cycles push the due date later.from 20 to 45 · whole numbers only · defaults to 28
What you get back
- Estimated due datemain answer
- Gestational age today
- Trimester
- Days until due date
- Estimated conception date
- Dating LMP (due date − 280 days)
- The 'week 0' the milestones count from.
What this assumes
- 280 days from LMP (Naegele's rule) with a ±1 day per day adjustment for cycles other than 28 days; 266 days from conception.
- Gestational age is computed against today's date on your device.
- Milestone weeks are typical windows and vary by provider and country. This is not medical advice; your care team's dating takes precedence.
About this calculator
A due date is a 40-week estimate counted from the first day of your last menstrual period — not from conception, which typically happens about two weeks later. Only about 4% of babies arrive on the day itself, but the date anchors every scan, screening and decision for the next nine months, so it's worth getting right.
The methods
- Last menstrual period (LMP) uses Naegele's rule: LMP + 280 days. It assumes ovulation on day 14 of a 28-day cycle. Open More options to enter your usual cycle length; a 32-day cycle pushes the date 4 days later, which is what a clinician would do.
- Conception or ovulation date adds 266 days. Use this if you tracked ovulation with tests or temperature.
- IVF transfer is the most precise: the embryo's age is known to the day. A day-5 blastocyst transfer adds 261 days; a day-3 transfer adds 263.
- Known due date works backwards from a scan-assigned date to show your current week, trimester and milestones.
How to read the results
Gestational age today is expressed in completed weeks and days ("12 weeks, 3 days"), the same way your midwife or OB will say it. Trimesters follow ACOG's convention: first through 13 weeks 6 days, second from 14 weeks to 27 weeks 6 days, third from 28 weeks. The milestone table lists common scans and screens by the week they usually happen — timings vary by country and provider, so treat them as a guide.
When ultrasound overrides the calendar
ACOG recommends that a first-trimester ultrasound be used to set the due date if it differs from the LMP date by more than 5 days before 9 weeks, or more than 7 days between 9 and 13 weeks 6 days. Once a due date is set by an early scan, it shouldn't be changed by later scans, even if the baby measures big or small. If you've had that scan, enter its date with the "Known due date" method.
A note on precision
Term is a five-week window: early term 37–38 weeks, full term 39–40, late term 41, post-term from 42. Most spontaneous births happen between 38 and 41 weeks. Think of your due date as the middle of that range, and the milestone dates as approximate.
Frequently asked questions
▸How is a due date calculated?
By Naegele's rule: the first day of your last period plus 280 days (40 weeks), adjusted for cycle length. From a known conception date it's 266 days. IVF pregnancies count from the transfer date minus the embryo's age.
▸Why does pregnancy count from my last period if I wasn't pregnant yet?
Because most people know that date and few know when they ovulated. The convention adds about two weeks before conception, which is why a 40-week pregnancy is only 38 weeks of fetal development.
▸How accurate is a due date?
Only around 4% of babies arrive on the due date; about 70% arrive within 10 days of it. A first-trimester ultrasound is accurate to about ±5 days, and it takes precedence over the LMP if they disagree significantly.
▸How many weeks pregnant am I?
Count from the first day of your last period, or from your due date minus 280 days. The calculator shows it in completed weeks and days, the format your care provider uses.
▸When does each trimester start?
First: weeks 0 to 13w6d. Second: 14w0d to 27w6d. Third: 28w0d until birth. Different sources sometimes draw the lines a week earlier or later.
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