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Both calculators run independently — change the inputs on either side to compare results.

Due Date Calculator (Naegele's Rule)

Estimate your due date from your last menstrual period using Naegele's rule, adjusted for your actual cycle length and luteal phase so a non-28-day cycle isn't misdated.

Days since first day of last period (LMP) (days)

Average menstrual cycle length (days)

Luteal phase length (days)

Pregnancy

Pregnancy Weeks to Months Converter

Convert pregnancy weeks and days into months and identify your trimester, using either calendar months or four-week 'lunar' months — the two conventions that cause confusion.

Completed weeks of pregnancy (weeks)

Additional days (days)

Month convention

Key differences

	Due Date Calculator (Naegele's Rule)	Pregnancy Weeks to Months Converter
Category	Pregnancy	Pregnancy
Inputs required	3	3
Result	Days until estimated due date (days)	Months and trimester
What it does	Estimate your due date from your last menstrual period using Naegele's rule, adjusted for your actual cycle length and luteal phase so a non-28-day cycle isn't misdated.	Convert pregnancy weeks and days into months and identify your trimester, using either calendar months or four-week 'lunar' months — the two conventions that cause confusion.