Due Date Calculator
Your estimated due date and how far along you are, from your last period, conception, IVF or a scan.
Works in your browser. The dates you type are not sent to us or stored.
Work it out from
A cycle is from the first day of one period to the first day of the next. 28 days is the usual figure; a longer cycle moves the date later.
Dates along the way
| Stage | Weeks | Date |
|---|
An estimate: most babies arrive in the weeks around the due date, not on it. Your doctor or midwife sets the date used for your care. Worked out in your browser; the dates you type are not sent to us or stored.
Due Date Calculator at a glance
- Price
- Free
- Data sent to us
- None, it runs in your browser
- Sign-up
- Not needed
- Works from
- Last period, conception, IVF, scan, due date
- Gives
- Due date, weeks pregnant, trimester, key dates
- Rules
- ACOG Committee Opinions 700 and 579
How to use Due Date Calculator
- Choose what you knowPick Last period, Conception, IVF transfer, Ultrasound or Due date.
- Type the dateChoose the date. For Last period, set your usual cycle length; for IVF, the embryo's age; for Ultrasound, the weeks and days on the report.
- Read the datesThe estimated due date, how far along you are today and the dates along the way appear at once.
Choose what you know: the first day of your last period (with your cycle length), the date of conception, an IVF embryo transfer, the age given at an ultrasound, or a due date you already have. The estimated due date appears with the weekday, how many weeks and days pregnant you are today, the trimester, the time to go and the likely conception date, plus a list of the dates along the way: the end of the first trimester, halfway, the third trimester, and early, full and late term as ACOG defines them.
How it works
Due Date Calculator is a web page that does its work on your own device. Everything you type or choose is worked out by your browser and never sent to a server, so nothing is stored and there is nothing to delete. There is no account, no sign-up and no limit on how often you use it.
Straight to one job
Conception Date Calculator · IVF Due Date Calculator
How a due date is worked out
A pregnancy is counted from the first day of the last menstrual period, about two weeks before conception, and the estimated due date is 280 days, or 40 weeks, after it. That convention, described by the American College of Obstetricians and Gynecologists in Committee Opinion 700, Methods for Estimating the Due Date, assumes a 28-day cycle with ovulation on day 14. With a longer or shorter cycle, ovulation usually moves by the difference, so this calculator moves the due date the same way: a 32-day cycle gives a date four days later.
| You know | Due date |
|---|---|
| First day of the last period | That date + 280 days, adjusted for the cycle length |
| Date of conception | That date + 266 days |
| IVF transfer, day-5 embryo | Transfer date + 261 days |
| IVF transfer, day-3 embryo | Transfer date + 263 days |
| Ultrasound age on a date | Scan date + (280 days − the age at the scan) |
Weeks, trimesters and term
Weeks of pregnancy are written as weeks and days, so 12 weeks 3 days means 87 days since the first day of the last period. The first trimester runs to the end of week 13, the second to the end of week 27, and the third from week 28 until birth. ACOG's Committee Opinion 579, Definition of Term Pregnancy, names the weeks around the due date: early term from 37 weeks 0 days to 38 weeks 6 days, full term from 39 weeks 0 days to 40 weeks 6 days, late term from 41 weeks 0 days to 41 weeks 6 days, and postterm from 42 weeks on.
Why an ultrasound date can differ
Dating from the last period depends on remembering the date and on when ovulation really happened. An ultrasound in the first trimester measures the baby and is the more accurate way to date a pregnancy, so your doctor or midwife may change the due date after the first scan. Once a due date has been set from an early scan, it is normally not changed again; choose Ultrasound here and type the age from the report to match it.
What this calculator is not
- Medical advice. It does the date arithmetic; the date your care is based on is the one your doctor or midwife gives you.
- A prediction of the birth day. A due date marks 40 weeks; full term is a two-week window, and many babies arrive before or after it.
What it does
- Five ways in: last period, conception, IVF transfer, ultrasound, known due date
- Cycle length from 20 to 45 days
- Day 3, 5 and 6 embryo transfers
- Weeks and days pregnant today, trimester and time to go
- Key dates: trimesters, halfway, early, full, late and postterm
- Rules from ACOG Committee Opinions 700 and 579
- Nothing sent or stored
Questions
How is a due date calculated?
By convention it is 280 days (40 weeks) after the first day of your last menstrual period, as described in ACOG Committee Opinion 700. That assumes a 28-day cycle; the calculator moves the date by the difference for a longer or shorter cycle.
How do I calculate my due date from conception?
Add 266 days (38 weeks) to the date of conception. Choose Conception and type the date.
How is an IVF due date calculated?
From the transfer date and the embryo's age: 261 days after the transfer of a day-5 embryo and 263 days after a day-3 embryo, per ACOG Committee Opinion 700. Choose IVF transfer and pick the embryo's age.
How many weeks pregnant am I?
Count the days since the first day of your last period and divide by 7; the remainder is the extra days. The calculator shows it for today as weeks and days.
What do early term, full term and late term mean?
According to ACOG Committee Opinion 579, early term is 37 weeks 0 days to 38 weeks 6 days, full term 39 weeks 0 days to 40 weeks 6 days, late term 41 weeks 0 days to 41 weeks 6 days, and postterm from 42 weeks.
Why did my doctor give me a different due date?
An ultrasound in the first trimester dates a pregnancy more accurately than the last period, so the date may be changed after an early scan. Choose Ultrasound and type the age from the report to match it. Always use the date your doctor or midwife gives you.
When does each trimester start?
The first trimester runs to the end of week 13, the second from week 14 to the end of week 27, and the third from week 28 until birth.
Is anything sent anywhere?
No. The dates you type are worked out in your browser and are not sent to us or stored.
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