My Bloom BuddyWhen is my next period?
Enter the first day of your last period and your cycle length. You'll get your next expected date — and the two after it — so nothing catches you out. It all runs in your browser: nothing is stored or sent.
Most cycles are 24–38 days. Not sure? Leave it at 28.
Enter your dates to see your bloom.
How the date is worked out
Your cycle is counted from the first day of one period to the first day of the next. So your next period is simply your last start date plus your cycle length. If your period began on the 4th and your cycle runs 29 days, the next one is due 29 days later — not 29 days after your period ended, which is the most common way people get this wrong.
Why the estimate moves
A predicted date is an average doing its best. Real cycles shift, and there is nothing wrong with you when they do. The usual culprits are stress, illness, disrupted sleep, travel across time zones, a change in weight or training load, and the natural irregularity of the years after your first period and approaching menopause.
A period arriving a few days either side of the estimate is ordinary. What is worth paying attention to is a change in your own pattern that lasts — which is exactly what tracking makes visible, and guessing does not.
Worth a conversation with a professional
- Your period is more than a week later than expected and pregnancy is possible
- You have missed three or more periods in a row
- Your cycles suddenly become much shorter, much longer, or much less predictable
- Bleeding is unusually heavy, or comes with severe pain or large clots
None of these mean something is wrong. They mean it is worth someone qualified taking a look.
These are estimates from a simple average cycle and will not match every body. This calculator is for gentle awareness only — it is not medical advice and not a form of birth control, and should never be used to prevent or achieve pregnancy.
Common questions
How do I calculate when my next period is due?
Take the first day of your last period and add your cycle length. If your period started on the 4th and your cycle is 29 days, your next period is due on the 2nd of the following month. The calculator on this page does that for you, and shows the two dates after it as well.
How accurate is a period prediction?
It is an estimate, not a schedule. Predictions are most reliable when your cycles are fairly consistent, and least reliable in the year or two after your first period, approaching menopause, or during a stretch of illness, travel, heavy training, or stress. Treat the date as a rough heads-up rather than a promise.
Why is my period late when the calculator said today?
Cycles are a rhythm, not a metronome. A period arriving a few days either side of the estimate is completely ordinary, and a single unusual month happens to almost everyone. If your period is more than a week later than expected, if you have missed three or more in a row, or if there is any chance of pregnancy, it is worth speaking to a doctor or nurse.
What if I do not know my cycle length?
Leave it at 28 days for a first estimate — that is the usual default. For a more accurate number, use the cycle length calculator, which works it out from the dates your last few periods started.
Can I use this to avoid pregnancy?
No. This is an awareness tool, not a contraceptive. Cycle-based estimates are not reliable enough to prevent pregnancy, and should never be used for that. Speak to a healthcare professional about contraception that suits you.
Not sure of your cycle length? Work it out from your last few period dates with the cycle length calculator, then come back here for your date.
Or stop doing the arithmetic.
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