Step 1
Your last period
Tell the app the first day of your last period, or skip it. Track then shows the day of your cycle.
Period calendar
A period calendar that marks your next period as a range
Period days, flow and the symptoms around them sit on one month view. From the cycles you have logged, the app shades the days your next period is likely to start, and widens that window when your cycles vary.
The short answer
Her Good Days keeps a free period calendar on your phone: each period day, its flow, spotting and the symptoms you logged, month by month.
Your next period is estimated from the average of your own recent cycle lengths and shown as a range of days. Tap any date to see everything you logged on it. You can start without an account.
Set it up in three taps
Step 2
Day one of the next
Tap + Log, then Period. For regular cycles it is first in the menu.
Step 3
See the month
Open Track, then Cycle. Period days are filled in and your next period is outlined as a range.
What does the calendar show?
| Mark | What it means |
|---|---|
| Filled day | A period day you logged, darker for heavier flow |
| Outlined days | The window your next period is likely to start in |
| Small dot | Spotting between periods |
| Symptom dots | Cramps, PMS, headaches, hot flashes or any symptom you logged that day |
| Ring | Today |
Tap a date and a sheet opens with that day's entries: flow, symptoms, mood, sleep and notes. You can edit or add from there, which is how most people fill in a period they forgot.
How does the next-period predictor work?
It averages your recent cycle lengths, counted from the first day of one period to the first day of the next, and counts forward from your last start date. Today shows a countdown, and the calendar outlines the likely days.
When your cycles have been close in length the window is narrow. When they jump around, it gets wider and the app says the estimate is less sure. The free estimator on this site uses a fixed cycle length you type in; the app uses your own history.
An estimate only. A predicted period cannot tell you when you are fertile or when pregnancy is unlikely. Do not use it as birth control.
What if my periods are irregular?
Keep logging the first day of each one. In Insights, a cycle-length chart shows every cycle as a bar, so a 24-day cycle followed by a 41-day one is easy to see and easy to show a doctor. Periods that turn irregular, lighter or heavier are often one of the first signs of perimenopause.
Which life stages see the calendar?
| Stage | How the calendar behaves |
|---|---|
| Regular cycles | Period first in the Log menu, estimate and countdown on Today |
| Teens, 13 to 17 | Calendar and next-period estimate, with no fertile-window features |
| Trying to conceive | Ovulation test results appear on the day you log them |
| Pregnancy | Predictions pause and your history is kept; appointments go on the calendar |
| After birth | When a period is logged, the app offers to start the cycle calendar again |
| Periods stopped | The cycle view becomes "Last period", with days since your last one |
Related
Sources
Checked October 30, 2026. How we check health facts
Questions
Is the period calendar free?
Yes. The calendar, the estimate, your full history and the cycle chart cost nothing, and there is no premium tier.
Can I add a period I forgot to log?
Yes. Tap the day on the calendar and add it. The estimate for your next period updates straight away.
Does the calendar show fertile days?
For regular or changing cycles it shows estimated fertile days, never in teen mode. They are estimates and not birth control. If you are trying to conceive, the app also logs ovulation test results. For a rough ovulation date, try the free ovulation estimator on this site.
Can I rely on the predicted date for birth control?
No. It is a guess from past cycles and says nothing about when you can or cannot get pregnant.
Does it sync with Apple Health?
If you allow it, period days you log can be written to Apple Health or Health Connect, and flow saved there by another app can be read in.
Start with today
Her Good Days is free, with no third-party ads and nothing to subscribe to. Free on iPhone and Android.