Due Date Calculator
Estimate your baby’s expected delivery date using Naegele’s rule from your last menstrual period or known conception date.
Accurately calculate your baby’s estimated due date (EDD) based on last period, conception date, or ultrasound dating.
See also: Pregnancy Calculator, TDEE Calculator (Total Daily Energy Expenditure), 1RM Calculator (One-Rep Maximum)
How it is calculated
Naegele’s Rule: EDD = First Day of LMP + 1 Year − 3 Months + 7 Days
Worked example: Calculating Due Date from Last Menstrual Period of July 1
LMP: July 1, 2026. Standard 28-day cycle.
- Add 280 days (40 gestational weeks) to the first day of your last menstrual period.
- Month duration count: July (30 days remaining), Aug (31), Sep (30), Oct (31), Nov (30), Dec (31), Jan (31), Feb (28), Mar (31) = 273 elapsed days through March 31.
- Remaining days to reach 280: 280 − 273 = 7 days in April.
- Total duration: Exactly 280 days from LMP to delivery date.
Estimated Due Date: April 7, 2027.
How to Use This Calculator (Step-by-Step)
- Choose whether to calculate from your last menstrual period or a known conception date.
- Enter the date and your average cycle length.
- Note your estimated due date and recommended ultrasound dating windows.
Frequently asked questions
What is Naegele’s rule?
Naegele’s rule is the standard clinical method for estimating delivery date: add one year, subtract three months, and add seven days to the first day of the last menstrual period.
How is the 280-day count worked out?
The worked example adds 280 days, or 40 gestational weeks, to the first day of the last menstrual period. Counting month by month from a July 1 last period reaches 273 elapsed days by March 31, leaving 7 days into April, for an estimated due date of April 7, 2027.
Can I calculate from a known conception date instead?
Yes. The calculation method input offers the first day of the last period or an exact conception date, so if you know the conception date you can select that method and enter it instead of a last period date.
Does my cycle length change the result?
Yes. The calculator asks for your average cycle length, between 20 and 45 days, alongside the reference date, because a cycle shorter or longer than the standard 28 days shifts the estimated date. Enter your own average rather than assuming 28 days.
Will my baby be born on the estimated due date?
Not necessarily. Due dates are estimates, and spontaneous labor commonly begins anywhere between 37 weeks and 42 weeks, so treat the date as a planning estimate rather than a fixed appointment.
Is this calculator medical advice?
No. Calculations are estimates only, not medical advice or diagnosis, and gestational milestones vary across individuals. Always consult an obstetrician, midwife, or certified healthcare provider for medical guidance.