Due Date Calculator: Pregnancy Due Date and Weeks
Estimate your baby's due date from the first day of your last period, the conception date or an IVF transfer date. See how many weeks pregnant you are, your trimester and key milestones.
Enter a date to see your estimated due date.
About the Due Date Calculator
The Due Date Calculator estimates when your baby is due and shows how far along the pregnancy is today. You can start from the first day of your last menstrual period, from a known conception date, from the date of an IVF embryo transfer, or from a due date you already have. Alongside the due date you get the number of weeks and days of pregnancy, the current trimester, the days left to go, an estimated conception date, and a list of milestones such as the anatomy scan window and full term, each with its own date.
All dates are treated as whole calendar days, so the result is the same wherever you are and never shifts because of a time zone or a change to daylight saving time.
This is an estimate, not medical advice. Only about 4 percent of babies arrive on their due date, and most are born within two weeks either side of it. Please confirm your dates with a midwife or doctor, who may adjust them after an early ultrasound scan.
How to find your due date
Steps
- Choose what you know: Last period, Conception date, IVF transfer or Due date.
- Pick the date. For the last period, also enter your usual cycle length if it is not 28 days. For IVF, choose a day-3 or a day-5 embryo.
- Read the estimated due date, how far along you are today and the milestone dates below it.
Cycle length
The standard rule assumes a 28-day cycle with ovulation about 14 days before the next period. If your cycle is usually 32 days, ovulation tends to happen about four days later, so the due date moves four days later too. Enter any whole number from 20 to 45 days.
Naegele's rule and the IVF formulas
The classic method, known as Naegele's rule, adds 280 days, or 40 weeks, to the first day of the last period and corrects for the cycle length:
From a conception date the calculator adds 266 days, which is 38 weeks. An embryo transfer adds 263 days for a day-3 embryo and 261 days for a day-5 blastocyst, because the embryo is already three or five days old on the day it is transferred. From a known due date it works backwards: the last period was 280 days earlier and conception about 266 days earlier, which is what the Conception Calculator shows.
Worked examples
- Last period on 1 January 2026, 28-day cycle: the due date is Thursday, 8 October 2026.
- The same date with a 32-day cycle: the due date moves four days later, to Monday, 12 October 2026.
- Day-5 embryo transferred on 19 January 2026: 261 days later gives Wednesday, 7 October 2026.
Privacy
Nothing is uploaded; every calculation runs in your browser and never leaves your device. The dates you type are not saved and disappear when you close the page.
Related tools
Count the days between any two dates with the Date Calculator, or work out an exact age in years, months and days with the Age Calculator. The BMI Calculator helps when you track your weight before pregnancy.
Frequently asked questions
How is the due date calculated?
From the first day of your last period, the calculator adds 280 days, which is 40 weeks. This is Naegele's rule. If your cycle is longer or shorter than 28 days, the date moves by the difference, because ovulation usually happens about 14 days before the next period.
Can I calculate my due date from the conception date?
Yes. Choose Conception date and the calculator adds 266 days, or 38 weeks. Pregnancy is still counted from a last period about two weeks before conception, so the weeks shown include those two weeks.
How does the IVF due date work?
For a frozen or fresh embryo transfer, the embryo's age is known exactly. The calculator adds 263 days to the transfer date for a day-3 embryo and 261 days for a day-5 blastocyst, which gives the same 40-week pregnancy counted from an equivalent last period.
How accurate is a due date?
It is an estimate. Only about 4 percent of babies are born on their due date, and most arrive within two weeks either side. An early ultrasound scan measures the baby and is often used to confirm or adjust the date.
My cycle is irregular. Will the result be right?
It may be off, because the rule assumes ovulation about 14 days before your next period. If your cycles vary a lot or you are unsure of your last period, a dating scan from your midwife or doctor gives a more reliable date.
Is my information stored or sent anywhere?
No. The dates you enter stay in this page and every calculation runs in your browser. Nothing is uploaded or saved, and it is all gone when you close the page.