Question 1

What if my cycles vary?

Accepted Answer

Use an average of recent cycles; expect a wider uncertainty range.

Question 2

Can birth control change timing?

Accepted Answer

Hormonal contraception often alters bleeding patterns — predictions may not apply.

Question 3

When to see a doctor?

Accepted Answer

Seek care for sudden irregularity, very heavy bleeding, or missed periods with concern.

Period Calculator

Related calculators