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Due Date Calculator
About the Due Date Calculator
Estimate your baby's due date from the first day of your last menstrual period (LMP). The calculator adjusts for your cycle length and also shows an estimated conception date.
How to use the Due Date Calculator
- Enter the first day of your Last Period (LMP).
- Enter your average Cycle Length (Days). If your cycle is regular at 28 days, leave the default.
- Press Calculate to see your estimated due date and conception date.
Formula and method
Naegele's rule: due date = LMP + 280 days (40 weeks), adjusted by adding or subtracting the difference between your cycle length and 28 days. Conception is estimated at about 14 days after the LMP for a 28-day cycle.
Worked example
LMP on 1 January with a 28-day cycle gives a due date of 8 October. With a 32-day cycle the estimate moves 4 days later, to 12 October.
Tips
- Only about 4 percent of babies are born on their due date; most arrive within two weeks either side.
- A dating ultrasound is more accurate than LMP if your cycles are irregular. Your doctor or midwife will confirm the date.
Frequently Asked Questions
It is an estimate. Healthy pregnancies last between 37 and 42 weeks.
Use the pregnancy calculator with a conception date or ask your healthcare provider for an ultrasound date.