Period Calculator
Put in the first day of your last period, your usual cycle length, and how long your period lasts. This period calculator maps your next six periods, with the fertile window and ovulation day in between. No sign-up, and nothing you type leaves your browser.
- Fertile window
- 31 Jul – 6 Aug7-day window
- Next period
- 20 Augin 28 days
Based on a 28-day cycle and a 5-day period. Ovulation is estimated ~14 days before your next period.
Skip the manual maths.
Bleed predicts your next period on its own — free, and all on your phone.
July 2026
August 2026
September 2026
October 2026
November 2026
December 2026
What this period calculator does
Most people land here asking one thing: when is my period due. That's the job. Enter the first day of your last period, your cycle length, and how long your period lasts, and this next period calculator gives you the dates your next six periods should arrive on, not just the one after this. Think of it as a simple calculator for your whole period cycle rather than a single-date answer.
It's also a period calculator with ovulation folded in. The same maths that predicts your period marks the fertile window and the ovulation day in each cycle, so whether you're trying to conceive, steering clear of it, or just want a heads-up on when you'll feel like yourself again, it's all on one calendar.
Staring at the calendar wondering if you're late? Drop in your last period and check today against the predicted date. As an am-I-late period calculator it won't confirm anything on its own, but it'll tell you in seconds whether you're a day behind or properly overdue.
There's no baked-in 28-day assumption here. Move the slider to the length of your cycle, whether that's 24 days, 31 days, or anything in between, and every date moves with it. That makes it a period calculator that follows your real cycle length instead of an average that might not be yours.
How this is calculated
The maths is simple. Your cycle length is the gap from one period starting to the next, so your next period is just your last start date plus your cycle length. Repeat that six times and you have the next six periods.
Ovulation works backwards from there. The luteal phase, the stretch between ovulation and your period, holds fairly steady at around 14 days for most people, so ovulation lands roughly 14 days before your next period starts. On a 28-day cycle that's about day 14; on a 31-day cycle, closer to day 17. The fertile window covers the few days before ovulation plus the day itself, since sperm can hang around for several days.
These are the same calculations the Bleed app runs. The difference: the app learns your real cycle from what you log and sharpens the prediction over time. Here you get a clean estimate from the averages you type in.
Your data stays yours
This is an online period calculator that never sends your dates anywhere. The maths runs in your browser, on your device. Nothing you type is logged, stored, or sold, and it's gone the moment you close the tab. Same principle as the app.
It's an estimate
A calculator can point at the likely dates. It can't diagnose anything, confirm a pregnancy, or work as birth control. Periods shift with stress, illness, travel, and life, so if something feels off, see a professional.
Common questions
- Is this period calculator free?
- Yes, properly free. No account, no paywall, no upsell, and no data collection. The period calculator runs in your browser and forgets everything the second you close the tab.
- Can I use it as an 'am I late' period calculator?
- Sort of. It predicts when your period is due, so you can see at a glance whether you're early, on time, or overdue. It's a guide, not a pregnancy test. If you're late and that matters to you, take an actual test or talk to a doctor.
- Does it show ovulation as well as my period?
- Yes. It's a period calculator with ovulation included. Every predicted cycle also marks your fertile window and ovulation day, worked out from the cycle length you enter.
- What if I don't know my cycle length?
- Use your best guess. Most cycles run somewhere between 24 and 35 days, and this defaults to 28. If your period calculator cycle length is off by a day or two, the predicted dates shift by about the same, so a rough number still gets you close.
- How far ahead does it predict?
- Six cycles. You get your next period first, then the five after it, each with its own fertile window and ovulation day.
Want it to learn your actual cycle?
Bleed tracks what you log and predicts your period and ovulation on its own — all on your phone.
iOS only. Your data never leaves your phone.