Ovulation Calculator

How to use

1. 1Enter the first day of your last menstrual period (LMP) in the date picker. Use the first day you started bleeding, not the day it ended.
2. 2Enter your average cycle length in days (from first bleed to first bleed). The default is 28; the field accepts 21 to 45.
3. 3Optional: adjust the Luteal phase field if you know your luteal length from a basal body temperature chart or fertility app. The default is 14 days.
4. 4Pick how many cycles to project (default 6). The tool returns one row per cycle.
5. 5Read the Today panel for the current cycle phase (menstrual, follicular, fertile, ovulation, or luteal) and a day count to the next ovulation and next period.
6. 6Read the Current cycle card for the period dates, the six-day fertile window, the peak-fertility days, ovulation day, the next period date, and the pregnancy due date if conception occurs.
7. 7Use the Cycle projection table to see every upcoming cycle at a glance. The row containing today is highlighted in blue.
8. 8Click Copy summary for a plain-text version of the current cycle, or Copy table (TSV) to drop the full projection into a spreadsheet.

About this tool

Ovulation Calculator estimates the most fertile days of a menstrual cycle from two simple inputs: the first day of the last menstrual period (LMP) and an average cycle length. It projects the ovulation date, the six-day fertile window, the peak-fertility days, the next period date, and a pregnancy due date if conception occurs in the current cycle, then repeats the projection for as many upcoming cycles as you ask for (up to twelve). The math is the standard textbook model used by Clearblue, the NHS, WebMD, and most clinical fertility apps: ovulation lands at next period minus the luteal phase length (14 days by default, adjustable from 9 to 18 to match an individual chart), the fertile window covers the five days before ovulation plus ovulation day itself (a six-day span backed by NICHD and WHO studies showing sperm can survive in the female reproductive tract for up to five days while the released egg stays viable for about 24 hours), the peak window is ovulation minus two through ovulation (the three days with the highest chance of conception), the next period falls one full cycle length after the LMP, and the pregnancy due date if conception occurs is ovulation plus 266 days, which equals LMP plus 280 days for a default 28-day cycle (Naegele's rule). A live today panel classifies the current calendar date into the matching cycle phase (menstrual, follicular, fertile window, ovulation, or luteal) and reports the next ovulation and next period dates with a friendly day count. A projection table lists every upcoming cycle with period start, fertile window, ovulation day, next period, and the conception due date, with the row containing today highlighted in blue. A copy-summary button drops the full plan into plain text for a notes app, calendar invite, or fertility journal, and a TSV copy button hands the projection table to a spreadsheet for couples who want to drop it into Google Sheets or Excel. Useful for couples trying to conceive who want to time intercourse to the fertile window, for anyone tracking a menstrual cycle to predict the next period and PMS days, for users coming off hormonal contraception and trying to reestablish a pattern, for shift workers and travelers who want a clean calendar export, and for general cycle awareness. Everything runs locally in your browser; the LMP, cycle length, luteal phase, and number of cycles you enter never leave your device. This is a calendar planning tool that assumes a regular cycle and is not medical advice; real cycles vary, especially after a recent pregnancy, while breastfeeding, around perimenopause, or with conditions such as PCOS or endometriosis, so consult a qualified healthcare professional for medical decisions about fertility, contraception, or pregnancy.

Free to use. Works in your browser. No signup, no login.