Pregnancy Due Date Calculator
Estimate when a baby is due and how far along the pregnancy is today, from the first day of the last period, the conception date or an IVF transfer date.
Result
Enter your values and select Calculate to see the result.
How to use this calculator
- Choose what you know: the first day of your last menstrual period (LMP), the conception date, or an IVF embryo transfer date.
- For LMP, enter your average cycle length if it is not 28 days.
- The result shows the estimated due date, how many weeks pregnant you are today and when each trimester starts.
Formula
- From LMP (Naegele’s rule):
due date = LMP + 280 days + (cycle length − 28) - From conception:
due date = conception + 266 days - From IVF transfer:
due date = transfer + 266 − embryo age(day 3: +263 days, day 5: +261 days)
Pregnancy is counted from the LMP, so “weeks pregnant” is about two weeks more than the time since conception.
Worked example
Last period on 1 January 2024
With a 28-day cycle, 1 January 2024 + 280 days = 7 October 2024. On 1 March 2024 the pregnancy would be 8 weeks and 4 days.
A day-5 IVF transfer
A transfer on 20 January 2024 + 261 days also gives 7 October 2024.
Assumptions and limitations
- This is an estimate. Only about 1 in 20 babies is born on the due date; most arrive within two weeks either side.
- An early ultrasound dating scan is more accurate than the LMP method, especially with irregular cycles.
- This tool is not medical advice. Your midwife, doctor or clinic will confirm your dates.
Frequently asked questions
Why is pregnancy 40 weeks if conception happens around week 2?
By convention, pregnancy is dated from the first day of the last period, about two weeks before ovulation and conception.
What if my cycles are irregular?
The LMP method is less reliable. Use a conception date if known, or rely on the date from an early ultrasound scan.