What does the Period Calculator work out?

Your next few period start dates. It is one of the Health & Fitness tools on Mondo Knows.

How is the Period Calculator calculated?

You get an instant answer with the working shown underneath.

Do I need to sign up, and is my data stored?

No sign-up, and nothing you type is sent anywhere. The calculation runs in your own browser, so the figures stay on your device and the page works offline once loaded.

Mondo Knows Tools

Period Calculator

Your next few period start dates. Use the free period calculator below to get an instant answer, with the formula shown so you can check the maths and trust the result. Free, private, and no sign-up.

First day of last period

Average cycle length

days

Period length

days

How many to predict

Mondo says

Choose the first day of your last period.

Period Calculator: common questions

What does the Period Calculator work out?: Your next few period start dates. It is one of the Health & Fitness tools on Mondo Knows.
How is the Period Calculator calculated?: You get an instant answer with the working shown underneath.
Do I need to sign up, and is my data stored?: No sign-up, and nothing you type is sent anywhere. The calculation runs in your own browser, so the figures stay on your device and the page works offline once loaded.

Mondo also knows

Ovulation CalculatorOvulation day and the fertile window.🌿 Health & Fitness Pregnancy CalculatorHow far along you are and the milestones ahead.🌿 Health & Fitness Pregnancy Weight Gain CalculatorThe recommended weight-gain range for your pregnancy.🌿 Health & Fitness Protein CalculatorDaily protein target based on weight and training.🌿 Health & Fitness

Estimates for general guidance only. This is not financial, medical or legal advice. Everything runs in your browser and nothing you type is stored.