What is Period?
The Period Calculator predicts your next menstrual period, ovulation date, fertile window, and PMS start based on your cycle history. This is one of the most searched health calculators globally, especially in India.
A typical menstrual cycle lasts 28 days (range: 21-35 days). Day 1 is the first day of bleeding. Ovulation usually occurs 14 days before the next period starts. The fertile window spans 6 days around ovulation. PMS symptoms typically begin 7-10 days before the period.
Tracking your cycle helps with: pregnancy planning, avoiding pregnancy (though not reliable as sole contraception), predicting PMS, identifying irregular cycles that may need medical attention, and general health awareness.
For pregnancy planning, use our Ovulation Calculator for a more detailed fertile window analysis, or the Conception Date Calculator if you're already pregnant.
Formula
Next Period = Last Period Date + Cycle Length Period Ends = Next Period + Period Duration - 1 Ovulation = Last Period + (Cycle Length - 14) Fertile Window = Ovulation - 5 days to Ovulation + 1 day PMS Starts = Next Period - 7 days
Example — Last period March 15, 28-day cycle: Next period: April 12 Ovulation: March 29 (day 14) Fertile window: March 24 – March 30 PMS may start: April 5
How to use this Period Calculator?
1. Enter the first day of your last period. 2. Enter your average cycle length (count day 1 to day 1 of next period). 3. Enter how many days your period usually lasts. 4. See predictions for next period, ovulation, fertile window, and PMS.