Guides

Understand your cycle

The team behind Plum writes these guides on how cycles work and how to track them well. Every claim links back to sources like ACOG, the NHS, Mayo Clinic, and the NIH. None of it is a substitute for advice from your own clinician.

What causes bleeding between periods?

Bleeding between periods usually isn't serious, but a doctor should always check it. See the common causes, what to write down and when to go.Read the guide

Why did I get two periods in one month?

Two periods in one month is often a normal cycle of 21 to 30 days. Here's how to tell, what a gap under 21 days can mean, and when to see a GP.Read the guide

How long is a normal menstrual cycle?

This guide explains what cycle length means, whether 28 or 35 days is normal, how many periods a year to expect, and what to get checked.Read the guide

How long does a period last?

A normal period lasts 2 to 7 days, and the average period length is 4. Read about 2-day and 7-day periods, bleeding past 8 days, and when to see a GP.Read the guide

Does cycle syncing work?

Cycle syncing means matching food, workouts and plans to your cycle phase. We look at what the research supports, what it doesn't, and what to track.Read the guide

What is the fertile window and how is it calculated?

The fertile window is the few days each cycle when pregnancy is possible. Here's how apps and clinicians estimate it, and where the estimates fall short.Read the guide

Irregular periods: common causes and when to see a doctor

Stress, travel, PCOS and thyroid problems are common reasons periods go irregular. Find out which signs need a doctor and how to track them.Read the guide

How to choose a period tracker that respects your privacy

Period apps hold your most sensitive data. This guide shows how to tell which trackers sell or share it, with a checklist for reading a privacy policy.Read the guide

Sharing your cycle with a partner

Share your cycle with a partner or friend only if you want to. We cover what's worth sharing, how much is too much, and four rules that keep it healthy.Read the guide

Do periods sync with friends?

Periods feel like they sync with friends and roommates, but the studies say no. Find out why the overlap happens and how to share dates instead.Read the guide

Period tracker apps that share with friends, compared

We compared fifteen cycle-sharing apps on who can join, what they see and what it costs. Most are built for one partner, but a few work for a whole group.Read the guide

Tracking your period when you have PCOS

PCOS makes cycles long and unpredictable, so app predictions often miss. Learn what to log and what a tracker should do about it.Read the guide

Tracking your period in perimenopause

Perimenopause makes cycles jump by a week or more and skip months, so app forecasts drift. Read what changes, what to log, and when to see a doctor.Read the guide

How to keep a period diary

A period diary is most useful when you fill it in the same day. Our guide covers what belongs in it, what to leave out, and what a clinician looks for.Read the guide

How to support your partner during their period

Written for partners, this guide covers what periods and PMS involve, the small things that help, the ones that backfire, and what a shared calendar does.Read the guide

How late can a period be?

Being a week late once in a while is ordinary. See what counts as late day by day, when a pregnancy test becomes reliable, and when to call a doctor.Read the guide

Tracking your cycle when you are trying to conceive

If you're trying to conceive, you have six fertile days each cycle. We cover what's worth tracking, what each sign tells you, and when to ask for help.Read the guide

Period tracker apps compared: Plum, Apple Cycle Tracking, Clue, Flo and Euki

We compare five period trackers on where your data lives, who sees it, how sharing with a partner or friends works, ads and price. Every source is linked.Read the guide

The best period tracker apps in 2026, one pick for each need

Seven period trackers, one pick for each need. Which ones are free, which have no ads, which keep your data on the phone, and which suit irregular cycles.Read the guide

When do periods come back after stopping birth control?

Most periods return within 3 months of stopping the pill, and later after the Depo shot. Here's why a first period runs late, and when to see a GP.Read the guide

Tracking your period when you have endometriosis

Endometriosis takes years to diagnose, and pain is the main sign. The guide covers what to log, how to make heavy and severe concrete, and what a GP needs.Read the guide

Tracking your period on birth control

Hormonal birth control changes what a period tracker can tell you. Learn what the break-week bleed is, what to log instead, and when to see a doctor.Read the guide