Compare calculators

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

Ovulation & Fertile Window Calculator

Pinpoint your likely ovulation day and fertile window from your cycle length, luteal phase, and the cycle day you're on today — based on the fixed-luteal-phase method.

Current cycle day (day 1 = first day of period) (day)

Average menstrual cycle length (days)

Luteal phase length (days)

Key differences

	Due Date Calculator (Naegele's Rule)	Ovulation & Fertile Window Calculator
Category	Pregnancy	Pregnancy
Inputs required	3	3
Result	Days until estimated due date (days)	Days until ovulation (days)
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.	Pinpoint your likely ovulation day and fertile window from your cycle length, luteal phase, and the cycle day you're on today — based on the fixed-luteal-phase method.