Irregular cycles
Tracking irregular periods
If your cycle doesn't stick to a schedule, one exact predicted date isn't much use. A range is more honest.
Most trackers assume a tidy 28-day cycle. Lots of people don't have one. If yours is 26 days one month and 34 the next, you need to see that spread.
How to track an irregular cycle here
- Write down the first day of your last three or four periods.
- Count the days between each pair and average them. That's your cycle length.
- Enter your most recent date and that average into the calculator, and treat every date as the middle of a window.
The gap between your shortest and longest cycle tells you how wide that window is. If it's a week, plan around the whole week rather than the single date on the card.
What the range means
Suppose your recorded cycles were 26, 31, 29 and 34 days. The average is 30, and the tracker shows your next period as a range from the 26-day mark to the 34-day mark. That range is the useful bit: it tells you when to keep supplies with you, without pretending to know the exact day.
The wider the range, the less you should trust any single predicted day. That includes the fertile window, which is worked out from the same average.
What the tracker won't do
It won't call your cycle "irregular" or "abnormal", and it won't guess at causes. It just reports your dates. Some variation is normal, especially in the first few years after periods start and in the years before menopause.
Missed a period?
If the expected date is more than a week gone, the calculator adds a Missed period section under your cycle day. It covers what to rule out first (pregnancy, contraception changes, a rough few weeks), the everyday things that tend to help (regular meals, enough food and healthy fats, steady walking rather than hard training, sleep), a realistic window for when a routine-related delay usually resolves, and a date by which to see a doctor if it still hasn't come.
Nothing on a website can promise a date your period will return. Three months without one, severe pain, very heavy bleeding or a positive pregnancy test are reasons to see someone sooner.
When to get advice
The NHS suggests seeing a GP if your periods suddenly become irregular and you're under 45, if your cycle is shorter than 21 days or longer than 35 days, if your period lasts more than 7 days, or if there's a difference of 20 days or more between your shortest and longest cycle. Get advice too if you bleed between periods or after sex, or if you might be pregnant.
Your dates can help in that appointment. Printing the calculator page from your browser gives you three months on one page.