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Enter the first day of the last menstrual period and get the estimated date of delivery by Naegele's rule, with each step shown. Add a second date to see gestational age as weeks and days. An exam study aid, not for clinical use.
Built for NCLEX-RNLeave blank to skip. Counts completed weeks and days since the LMP.
Naegele's rule assumes a 28-day cycle and a sure LMP. The estimated date of delivery is the expected birth date, give or take 2 weeks.
Pick the first day of the last menstrual period.
Pregnancy and newborn questions make up a steady slice of the NCLEX-RN. Encodr keeps the Naegele rule, the Apgar score and the rest of the maternal-newborn facts on a spaced-repetition schedule.
Get started freeNaegele's rule gives the estimated date of delivery (EDD) from the first day of the last menstrual period (LMP) in three steps: subtract 3 months, add 7 days, then adjust the year (move to the next calendar year). It assumes a 28-day cycle and a certain LMP, and the EDD is the expected birth date plus or minus 2 weeks, which allows for normal variation.
Worked examples: an LMP of 25 August 2026 minus 3 months is 25 May, plus 7 days is 1 June, and adjusting the year gives 1 June 2027. An LMP of 10 March 2026 minus 3 months is 10 December 2025, plus 7 days is 17 December 2025, and adjusting the year gives 17 December 2026. The year step is the one people skip, and it is the one exam writers like to test. Step-by-step, with more examples, in Naegele's rule: how to calculate a due date. The maternal-newborn units are in the free NCLEX-RN deck.
This tool is a study aid. Real dating of a pregnancy uses the care team's methods, which can include ultrasound.
Naegele's rule finds the estimated due date from the last menstrual period in three steps. Worked examples, the year step, assumptions and common mistakes.
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