How this late period calculator and tracker work
When you search for “why is my period late”, you usually have four questions. How late is it really? Should you take a test? What could be causing it? Does it need a doctor? This site answers all four in one place, starting with only the date of your last period and your usual cycle length. There’s nothing to install and no account to create, and what you type stays in your browser.
What the checker does with your dates
The sum is deliberately simple, so you can check it yourself. The tool adds your usual cycle length to the first day of your last period to find when your next one was expected, then compares that date with today. Up to three days either side counts as on time, because cycles naturally shift a little. Anything later counts as late, and 90 days or more since your last period is flagged as worth discussing with a doctor.
Using your own cycle length makes a real difference. The average cycle is about 28 days, and anywhere from 21 to 35 days is common. If yours usually runs to 33 days, a period can look five days late against the average when it’s actually on time for you.
From “how late” to “why”
The full late period checker goes further. It asks whether pregnancy is possible, whether you have any urgent symptoms, and whether anything has recently changed, such as stress, weight, training, sleep or contraception. It then shows the causes that fit your answers, along with sensible next steps.
You won’t see a percentage. A figure like “72% stress” would look scientific, but no one can honestly calculate that from a few checkboxes. You’ll see plain explanations instead, with anything urgent shown first. If pregnancy is possible, the checker explains when to test: home tests are most reliable from the first day of a missed period, and a negative result is worth repeating a few days later if your period still hasn’t come.
A period calculator that shows honest ranges
The period calculator estimates when your next periods are likely to start, for up to 12 months ahead. Each result is a date range, because small differences between cycles add up. If your cycles vary by about three days, your next period has a window of three days either side, and the fourth period ahead has a window of six. You can add the dates to your own calendar, with event titles that don’t mention periods, or print them. The ovulation calculator uses the same approach to estimate your likely fertile days. Neither should be used as contraception.
A private period tracker that learns your pattern
A calculator starts from an average, while a period tracker starts from you. Log your flow, symptoms, mood, cervical mucus and temperature in a few taps, and your record builds up month after month. The tracker uses the middle value of your last 12 cycles, so one unusual month doesn’t skew your prediction. Once you’ve logged three or more cycles, it measures how much your own cycle varies and uses that to set the width of your date range.
You also get a clear view of your shortest and longest cycles, how regular they are, and which period symptoms you log most often. If something looks worth raising, such as a very long gap, the tracker says so. Your log is stored in your browser, which means no one else holds a copy. It also means you’re responsible for keeping a backup, so the tracker makes that easy to do.
Checkers for what you’re noticing right now
A late period often comes with other questions, so the site includes a tool for each of the most common ones:
- Implantation bleeding vs period: compare the timing, colour, flow and cramps you’re experiencing with both patterns. If you’re noticing spotting before your period, this is a good place to start.
- Cramp relief planner: get steps matched to your pain level, and read what helps with period cramps in more detail.
- Discharge decoder: see how discharge before a period usually changes, and which changes are worth checking.
- Flow colour photo check: wondering why your period blood is brown? Your browser can read a colour from a photo of a pad, liner, tissue or cup, without uploading or saving the photo.
Guides that explain the answers
Each tool links to a plain-English guide with its sources listed. Learn how the period cycle works, what happens in each of the period phases, and why ovulation timing can change when your period arrives. If you’re comparing products, our unsponsored guides to the period cup, period panties and period swimwear cover what’s known, what isn’t, and what to check before you buy. We don’t recommend any brand.
Sharing your results, on your terms
Sometimes the most useful thing you can do with your data is show it to someone. Each calculator and checker can share its result through your phone’s share menu, by email, or as text to copy. In the tracker, you choose what goes into a summary for your doctor or partner: dates and cycle lengths are always included, while symptoms, temperature and notes stay out unless you tick them. You can preview the exact wording first, download a spreadsheet, or send a full backup to your other device. Whichever you choose, your data goes straight from your device to the app you pick, and never passes through this site.
What this tool can’t do
These tools can’t diagnose a condition, confirm or rule out pregnancy, or replace a clinician. They also can’t account properly for hormonal contraception, which changes your cycle. Every formula and limit is published, so you can judge the results for yourself.
See a GP if you’ve missed three periods in a row, if your periods have become irregular, or if you’ve missed a period and also have symptoms such as weight changes, tiredness or new facial hair. A late period usually has a simple explanation, but you never need a calculator’s permission to ask for help.
Looking for a different kind of period? We also have a short note on the refractory period and the Edo period.