Predict your upcoming period dates from your last period and cycle length.
How period is worked out
Enter the first day of your last period and your typical cycle and period length, and this calculator estimates when your next periods will start and how long they’ll last.
Cycles naturally vary, so use it as a general guide.
A worked example
On the values this calculator opens with, the days until next is 14. Underneath, Next period comes out at Aug 25 and Following period at Sep 22. Change any field and every figure updates as you type.
Step by step
- Enter the first day of your last period.
- Enter your cycle and period length.
- Read the next period dates.
The calculation
next period = last period + cycle length
repeat for following cycles
Frequently asked questions
How is my next period predicted?
By adding your cycle length to the start of your last period, then repeating for future cycles.
Why might my period be off?
Stress, travel, illness and hormonal changes can all shift timing, so predictions are approximate.
Is this a fertility or contraception tool?
No — it only predicts period timing and shouldn’t be relied on for contraception.