Due Date Calculator
Calculate your estimated due date (EDD) from the first day of your last menstrual period (LMP). The calculator adds 280 days, or 40 weeks, and names the weekday of the result.
How to use the Due Date Calculator
- Enter your numbers in the Due Date Calculator above.
- Press the Calculate Due Date button to see the result.
- To try other numbers, change any value and press the button again.
The EDD formulas
EDD = LMP + 280 days · · · For a cycle of X days: EDD = LMP + 280 days + (X − 28) days
The 280-day standard assumes a 28-day cycle with ovulation on day 14. The calculator has no field for cycle length. For a cycle of X days, add X − 28 days to its result yourself. Naegele's rule counts in calendar months instead. It adds a year, subtracts three months and adds seven days, and because months differ in length its date can land a few days later. For a last period that started on May 8, 2020, Naegele's rule gives February 15, 2021, while this calculator shows Friday, February 12, 2021.
Worked example
LMP February 10, 2026 with a regular 28-day cycle: EDD = November 17, 2026 (280 days later). LMP February 10, 2026 with a 32-day cycle: EDD = November 21, 2026 (add 4 days yourself for the longer cycle).
Frequently asked questions
How do I calculate my due date from my last period?
Add 280 days, or 40 weeks, to the first day of your last period. A last period that started on February 10, 2026 gives Tuesday, November 17, 2026, and that is what the calculator shows when you enter February 10, 2026. The NHS says pregnancy normally lasts 37 to 42 weeks from that first day. The 12-week scan estimates how far along you are more accurately, so go by the date your midwife or doctor gives you.
Why is my scan due date different from this one?
The calculator only knows the first day of your last period and assumes a 28-day cycle. A dating scan measures the baby, and Cleveland Clinic calls ultrasound the most reliable way to set a due date. ACOG Committee Opinion 700 says the due date should be set from the last period, the first accurate ultrasound or both, and changed after that only in rare cases. If the two dates differ, go by the one your midwife or doctor gives you.
What do early term, full term and postterm mean?
ACOG Committee Opinion 579 splits the weeks from 37 on into four groups. Early term runs from 37 weeks 0 days through 38 weeks 6 days and full term from 39 weeks 0 days through 40 weeks 6 days. Late term covers 41 weeks 0 days through 41 weeks 6 days, and postterm starts at 42 weeks 0 days. The date this calculator shows is 40 weeks 0 days, inside full term.
How many babies arrive on their due date?
Only about 4%, according to Cleveland Clinic. The due date marks 40 weeks from the first day of your last period, and the NHS says pregnancy normally lasts 37 to 42 weeks from that day.