How to track your period

What to track at minimum

• First day of your period. The first day of full flow, not spotting. This is the single most important data point.
• How many days bleeding lasts. Five days is typical; two to seven days is normal.
• Flow intensity. Light / medium / heavy is plenty of detail.

With just those three things tracked for three to six months, you’ll learn your typical cycle length, period length, and flow pattern.

What to track if you want more insight

• Cervical fluid changes — clear and stretchy near ovulation, drier in the luteal phase.
• Basal body temperature — a sustained rise of ~0.3–0.5°C confirms ovulation happened.
• Mood, sleep, energy — patterns often align with cycle phases.
• PMS symptoms — bloating, breast tenderness, cravings, headaches.
• Ovulation pain (mittelschmerz) — a brief sharp pain on one side mid-cycle.
• Sex — for fertility tracking, log dates of unprotected sex.

Three ways to actually do it

1. Paper calendar or journal

A simple paper calendar is the most private option: nothing touches the internet. Mark a dot or symbol on the first day of each period. Add brief notes for flow and symptoms. Takes 30 seconds a day.

2. A cycle-tracking app

Apps like Flo, Clue, Ovia, and Natural Cycles make logging easy and do prediction math for you. Watch for the privacy trade-off: many apps store your data on their servers. Read the app’s privacy policy before signing up — and only use one you trust.

3. The Period Tools calculator

If all you need is a quick prediction, our Period Calculator runs in your browser — no signup, no data stored anywhere, everything happens locally. Best paired with a paper or app long-term log so you can plug in your average cycle length.

Common tracking mistakes

A few habits quietly wreck the accuracy of your log:

• Logging the wrong day 1. Day 1 is the first day of full flow, not the day spotting starts. Counting spotting as day 1 makes your cycle look longer than it is.
• Tracking period-end to next-period-start. Cycle length is measured start-to-start, not end-to-start. The end-to-start gap will always read short.
• Giving up after one odd month. A single unusual cycle tells you almost nothing. Patterns only emerge over three to six months — don’t over-react to one outlier.
• Trusting an app’s prediction in month one. With only one cycle logged, an app is just using the 28-day population average, not your data. Predictions get good once you’ve fed it a few real cycles.
• Logging only the dates. Dates alone predict timing, but symptoms (flow, mood, pain, cervical fluid) are what reveal why an off month happened. A date with no context is a missed clue.

What patterns are worth paying attention to

• Consistent cycles shorter than 21 days or longer than 35 days
• Cycle length suddenly changing by more than a week
• Bleeding lasting more than 7 days or unusually heavy flow
• Spotting between periods that wasn’t there before
• Severe pain that interferes with daily life
• Skipping three or more periods without an obvious reason

None of these means something is wrong, but they’re worth mentioning to a healthcare provider — especially if you have data to show them.