Enter the first day of your last period and your average cycle length. The calculator estimates when your next period may begin and when ovulation may occur.

Important: These dates are estimates, not medical advice. Ovulation can change from one cycle to another. Do not use this calculator as your only method of birth control.

Which date should I enter?

Enter the first day your last period started, not the day it ended. A menstrual cycle is counted from the first day of one period to the first day of the next.

Can this predict pregnancy risk?

No calendar estimate can identify safe or unsafe days with certainty. Stress, sleep, illness, weight changes, hormones, medication, and irregular cycles can all change ovulation timing.

Use reliable contraception if you want to prevent pregnancy. If you are trying to become pregnant, ovulation tests or advice from a healthcare professional may provide more useful information.

When should I take a pregnancy test?

Follow the instructions supplied with the pregnancy test. Tests are generally more reliable from the first day of a missed period. If the result is negative but your period still does not begin, consider testing again or speaking with a healthcare professional.

When to seek medical advice

Speak with a healthcare professional if your periods stop for several months, become unusually frequent, change repeatedly, cause severe pain, or involve unusually heavy bleeding.

Frequently Asked Questions

Is this an ovulation calculator?
This calculator gives a possible ovulation date based on your cycle length, but ovulation can change from cycle to cycle.

Can I use this as a safe days calculator?
No. Calendar-based estimates cannot confirm safe days. Use reliable contraception if you want to prevent pregnancy.