What is the best period tracker for irregular periods in the UK?
Choose a tracker that shows ranges instead of one date, lets you log symptoms beside dates, and can summarise them for your GP. Splash widens its range when cycles vary, has PCOS and perimenopause settings, and makes its doctor report free; Flo keeps its doctor report in Premium. The NHS calls periods irregular when the gap is under 21 or over 35 days.
On this page 7 sections
What counts as an irregular period?
The NHS says periods are irregular if the gap between them is less than 21 days or more than 35 days. Common causes include puberty, approaching menopause, pregnancy, hormonal contraception, big changes in weight, stress, excessive exercise, and conditions such as PMOS (the new NHS name for PCOS) or thyroid problems.
A single odd cycle is common. A pattern is what matters, which is why a log you can show a GP beats memory.
What should an app do if my cycles are irregular?
- Show a range, not a date. One predicted day will be wrong most months. A window with a most-likely day is honest.
- Not call you “late” by default. If you have PCOS or are in perimenopause, a countdown to a missed period adds stress and no information.
- Let you log what goes with the dates. Flow, spotting, pain, mood, sleep and any medicine, so patterns are visible.
- Make a summary for your GP. A short report of cycle lengths and symptoms is what a short appointment needs.
- Be clear it is not contraception. Irregular cycles make calendar fertile-window estimates less reliable still.
How does Splash cope with irregular cycles?
Splash uses your own history rather than assuming 28 days, gives recent cycles more weight, and stops one unusual cycle from dragging every future date. If you tell it you have PCOS, are in perimenopause or are on testosterone, it starts with a wider range and never frames a long cycle as late. The doctor report is free, as are insights and every mode.
In our tests on made-up cycle histories, the range contained the real start far more often than a simple average did, at the cost of being wider. That is the trade: honest uncertainty, not a confident wrong date.
| Cycle type | Real start inside the range, simple average | Real start inside the range, Splash | Range width, Splash (days) |
|---|---|---|---|
| Regular | 59% | 82% | 5.8 |
| Irregular | 45% | 75% | 12.4 |
| PCOS-like | 30% | 77% | 32.6 |
| Perimenopause-like | 32% | 74% | 22.3 |
Splash’s own tests on synthetic (made-up) cycle histories, re-run with each app build. Real cycles are messier. Full method on the how-predictions-work page.
How do Flo, Clue and Apple compare for irregular cycles?
All three let you log symptoms. What differs is what costs money: Flo keeps its doctor report (iOS, last six months), cycle patterns and Symptom Checker (not available in the UK or EU) in Premium; Clue Plus holds its Conceive and Perimenopause modes; Apple Cycle Tracking is free and can export a PDF of your last 12 months for a healthcare provider. See the sourced comparison for the detail.
When to see a doctor
Questions people ask
Which period tracker is best for PCOS?
There is no single best. Look for wider ranges, no late-period countdown, symptom tags and a GP summary. Splash has a PCOS setting with these, free. PCOS, which the NHS now also calls PMOS, is diagnosed by a clinician, not an app. Use the log to describe your cycles and symptoms at your appointment.
Can a period tracker predict irregular periods?
Only roughly. With variable cycles, any app can give a range at best, and ranges are wide. Logging steadily helps, and adding LH tests or temperature improves ovulation estimates. Treat predictions as planning aids, and never as contraception.
How many cycles should I track before seeing a GP?
You do not need to wait for a set number if you are worried. The NHS suggests seeing a GP if your periods are irregular, last over 7 days, or come with other symptoms. Three or more months of logged dates and symptoms makes the appointment more useful.
Is the Splash doctor report free?
Yes. You can print it, save a PDF, or send your clinician an end-to-end encrypted link that expires after 24 hours, 7 days or 30 days. Flo keeps its doctor report in Premium. Splash cannot diagnose; the report just puts your cycle lengths, flow and symptoms in one place.
Sources
- NHS: Irregular periods (reviewed 26 Jun 2026) accessed 2026-10-28
- Flo help centre: What is included in Flo Premium (posted 4 Oct 2024) accessed 2026-10-28
- Clue support: What’s Clue Perimenopause mode? accessed 2026-10-28 (Clue blocks automated fetching; read through a search excerpt.)
- Apple Support: Track your menstrual cycle (Cycle Tracking), published 14 Sep 2026 accessed 2026-10-28
Splash makes one of the apps mentioned here, so every claim about another app links to its own page or an independent source. Spotted something wrong? Email us and we will fix it and note the change.
Keep reading
- Irregular cycles explained
- PCOS (now PMOS): signs and diagnosis
- Cycle length calculator
- Is my period normal? check
- How Splash predicts
- Doctor report
- Is my period tracker data private?
- Is there a period tracker that works without an account?
- How accurate are period tracker predictions?
- Which period tracker is best for perimenopause?
General information, not medical advice. Splash is not contraception, not a medical device and cannot diagnose, and it is not affiliated with the NHS. If you are worried, talk to a GP, pharmacist or sexual health clinic. How we write and check content.
Log it once, show your GP
Free predictions as ranges, a doctor report and no account.