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Estimate due date from your last menstrual period.
🤰 Naegele's rule: due date = LMP + 280 days. Only an estimate — only 5% of babies arrive on their due date.
This calculator estimates your pregnancy due date using Naegele's rule: add 280 days (40 weeks) to the first day of your last menstrual period. It also shows the likely conception date and current week.
Pregnancy is counted in weeks from the last period, not from conception. The "40 weeks" includes ~2 weeks before you actually conceived. Full term is anywhere from 37 to 42 weeks.
Only about 5% of babies arrive on their estimated due date. Most arrive within two weeks of it. First babies tend to arrive a few days late; subsequent babies often come earlier.
Disclaimer: This tool is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Results are estimates and should be discussed with a qualified healthcare provider before making health-related decisions.
The Pregnancy Due Date Calculator lets you figure out due date calculatorinstantly, without reaching for a spreadsheet or doing the math by hand. Whether you're planning a budget, checking a loan, or working through homework, the tool applies the correct formula behind the scenes and shows the result the moment you enter your numbers.
Unlike a static chart or table, this calculator adapts to your exact inputs. You can adjust any value and see the outcome update in real time, which makes it easy to compare scenarios — for example, "what if the rate were 1% lower?" or "what if I paid an extra $50 a month?"
Common uses: people reach for this tool when they need to find a due date from last menstrual period, pregnancy week by week calculator, naegele rule due date, or conception date from lmp.
Browser-based tools like this one have a few real advantages over installed software or manual methods:
The Pregnancy Due Date Calculator is based on the following formula:
Due date = LMP + 280 days
Variables: Due date = Estimated delivery date (calendar date) LMP = First day of the last menstrual period (calendar date) 280 days = 40 weeks of gestation
Naegele's rule: add 280 days (40 weeks) to the first day of the last menstrual period. Actual delivery varies by roughly two weeks either way; it is an estimate, not a guarantee.
Worked example: Step 1: LMP is January 10, 2026. Step 2: January has 21 days left after the 10th; then Feb 28, Mar 31, Apr 30, May 31, Jun 30, Jul 31, Aug 31, Sep 30 add 242 more, totaling 263 days through September 30. Step 3: 280 − 263 = 17, so the due date lands 17 days into October. Result: estimated due date October 17, 2026.
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