Compare calculators

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

Conception Date Estimate Calculator

Estimate how many days ago conception likely occurred from your last menstrual period, corrected for your cycle length and luteal phase rather than assuming day-14 ovulation.

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

	Conception Date Estimate Calculator	Ovulation & Fertile Window Calculator
Category	Pregnancy	Pregnancy
Inputs required	3	3
Result	Days since estimated conception (days)	Days until ovulation (days)
What it does	Estimate how many days ago conception likely occurred from your last menstrual period, corrected for your cycle length and luteal phase rather than assuming day-14 ovulation.	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.