Do You Know To Calculate Your Ovulation

Take notes of the period dates. That is the beginning and end dates of the periods for each month. 

This could help you find the irregularities and thus the proper cycle.

Example:
Period starts = 1st January
Next period starts = 3rd February
Days in between (including 1st Jan but not 3rd Feb) = 33 days.

Your menstrual cycle length is 33.

Match with the Chart:

Cycle length: 22 Ovulation: Day 8 Most Fertile: Days 7-9

Cycle length: 23 Ovulation: Day 9 Most Fertile: Days 8-10

Cycle length: 24 Ovulation: Day 10 Most Fertile: Days 9-11

Cycle length: 25 Ovulation: Day 11 Most Fertile: Days 10-12

Cycle length: 26 Ovulation: Day 12 Most Fertile: Days 11-13

Cycle length: 27 Ovulation: Day 13 Most Fertile: Days 12-14

Cycle length: 28 Ovulation: Day 14 Most Fertile: Days 13-15

Cycle length: 29 Ovulation: Day 15 Most Fertile: Days 14-16

Cycle length: 30 Ovulation: Day 16 Most Fertile: Days 15-17

Cycle length: 31 Ovulation: Day 17 Most Fertile: Days 16-18

Cycle length: 32 Ovulation: Day 18 Most Fertile: Days 17-19

Cycle length: 33 Ovulation: Day 19 Most Fertile: Days 18-20

Cycle length: 34 Ovulation: Day 20 Most Fertile: Days 19-21

Cycle length: 35 Ovulation: Day 21 Most Fertile: Days 20-22

Cycle length: 36 Ovulation: Day 22 Most Fertile: Days 21-23

Fertile Period:

Work out your ovulation and most fertile dates.

First day of last period = 3rd February
Cycle Length = 33
Ovulation (19 days later) = 22nd February
Most fertile (18-20 days later) = 21st and 23rd February

You are most fertile the day before, during and the day after.Since sperm can survive for up to seven days in the right conditions, you could be fertile before and after these days.