Compare calculators

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

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)

Pregnancy

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)

Key differences

	Ovulation & Fertile Window Calculator	Due Date Calculator (Naegele's Rule)
Category	Pregnancy	Pregnancy
Inputs required	3	3
Result	Days until ovulation (days)	Days until estimated due date (days)
What it does	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.	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.