Period Tracker

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How does a period tracker work?

A period tracker uses the dates of your previous periods to predict when your next one will arrive. The core calculation is simple: your average cycle length is calculated from your historical data, and that number is added to the first day of your last period to estimate the next start date. Over time, with more data points, predictions become increasingly accurate for people with consistent cycles. Our tracker uses your cycle length and last period date to generate your personalised forecast.

What is a normal menstrual cycle?

The average menstrual cycle is 28 days, but anything from 21 to 35 days is considered within the normal range for adults. The length of your period itself typically ranges from 2 to 7 days. Cycle length can vary from month to month by a few days even in healthy people — this is normal. Significant variation (more than 7–9 days between your shortest and longest cycles) may warrant a conversation with a healthcare provider, as it can sometimes indicate hormonal imbalances or conditions like PCOS.

What affects cycle regularity?

Many factors influence the timing of your period. Stress is one of the most common disruptors: it affects the hypothalamus, which controls the hormones that drive the menstrual cycle. Sudden changes in weight — either loss or gain — can delay or stop periods. Intense physical training, particularly endurance sports, can cause hypothalamic amenorrhoea (absent periods) due to energy deficiency. Illness, travel across time zones, changes in sleep patterns, starting or stopping hormonal contraception, and perimenopause can all alter cycle timing as well.

Tracking beyond dates: what else to log

The most useful period trackers go beyond just start and end dates. Logging symptoms — cramps, bloating, breast tenderness, mood changes, energy levels, skin changes — over several months reveals patterns that can be helpful for managing premenstrual symptoms and for conversations with a doctor. Noting the heaviness of your flow (light, medium, heavy) can also flag changes worth discussing: a sudden increase in heaviness can be related to fibroids, adenomyosis, or hormonal shifts.

When to see a doctor about your period

Consult a healthcare professional if: your periods suddenly become much heavier or lighter than usual; you experience severe cramping that is not relieved by over-the-counter pain relief; your cycle becomes very irregular when it was previously regular; you miss three or more consecutive periods and are not pregnant; or you experience bleeding between periods or after sex. These symptoms do not necessarily indicate a serious condition, but they are worth investigating.