How the app calculates: interval, duration and the 5-1-1 check

The rule check in Contraction Timer uses only the times you tap. From these times the app works out the interval between contraction starts, the duration of each contraction and how long your rhythm has been regular. Every number on this page comes from the app’s code as of October 2026.

Recording a contraction

In the timer you tap the big button when a contraction starts and again when it eases. The app stores two times for each contraction, its start and its end. A contraction that is still running only counts once you’ve tapped its end.

If the end is hard to tell, switch to “Start only” in the settings. You then tap once per contraction, and the app knows only the intervals. In this mode the rule check looks at interval and regularity, and the missing duration doesn’t hold the alert back. Contractions you already recorded stay as they are when you switch.

When you tap start and end, the app asks whether the contraction was mild, medium or strong. You can turn the question off, and the answer plays no part in the rule check. If you tapped by mistake, edit the start and end in the contraction list or delete the contraction. Deleted contractions no longer count.

Interval and duration: what the app works out

Duration runs from the start of a contraction to its end. The app measures the interval from the start of one contraction to the start of the next. The rest in between is part of it. How to do the same with a clock and paper is explained in how to time contractions.

For the “Last hour” panel in the timer and for the rule, the app uses averages. It takes every contraction that started in the last 60 minutes, and older ones drop out of the averages. The rule needs at least three contractions, which gives two intervals. For the duration it needs two contractions with a tapped end.

How the app checks 5-1-1 and 4-1-1

During setup the app asks which rule your hospital or midwife gave you. You can pick 5-1-1, 4-1-1 or a custom rule. For 5-1-1 and 4-1-1, three conditions have to hold at the same time:

Condition	5-1-1	4-1-1
Average interval over the last hour	5:30 minutes or less	4:30 minutes or less
Average duration over the last hour	at least 54 seconds	at least 54 seconds
Rhythm regular for	at least 60 minutes	at least 60 minutes

Neither rule is exact. Lamaze International calls them general guidelines and says the answer to when to go in “isn’t a perfect science”. The app therefore leaves some slack: 30 seconds on the interval and 10 percent on the duration.

For the app, regular means:

• No interval is longer than the rule’s interval plus two minutes. For 5-1-1 that’s seven minutes, for 4-1-1 six.
• Every contraction lasts at least 45 seconds, three quarters of a minute. In “Start only” mode this check is skipped.

To check this, the app walks back from your latest contraction until an interval is too long or a contraction too short. The time counts from the start of the first contraction in that run until now. A longer pause ends the run, and the hour starts over. Contractions that have already dropped out of the averages still count for the run.

If interval and duration fit and only time is missing, the timer shows for how many minutes the pattern has matched.

4-1-1 needs contractions closer together than 5-1-1. With 4-1-1 the alert therefore comes at the same time as with 5-1-1 or later, never earlier. You can try the check with the online timer on this site. It uses the same function, fixed to 5-1-1, and keeps your data in your browser only.

Custom rules and the weeks before 37

If your hospital gives you other numbers, enter them as a custom rule:

• Interval: 1 to 60 minutes
• Duration: 0 to 300 seconds; at 0 any duration counts
• Period: 1 to 360 minutes

The same slack applies as for 5-1-1. The app averages over the last hour, or over your period if it’s shorter. With a period of two hours, the rhythm still has to stay regular for the full two hours.

If you’ve entered your due date and you’re not yet 37 weeks (37+0), a separate rule replaces yours. The app then alerts you once four contractions have started within the last 60 minutes. Interval and duration don’t matter for it. Don’t wait for this alert, though. Under 37 weeks, the NHS says to call your maternity unit right away if you think labor is starting.

When the alert comes and what it offers

While the app is open, it checks the rule every few seconds. When the rule is met, a screen appears that says “It’s time to call your clinic.” Below it you see the average interval, the duration and how long your rhythm has been regular. If vibration is on, the phone vibrates.

The alert gives you four options:

• The call button opens a call to the number you saved and closes the alert. Without a saved number it takes you to the field where you add one.
• “Notify partner” opens your phone’s share menu with a ready-made message. The app stores nothing.
• “Keep tracking, remind me later” hides the alert. It comes back after 15 minutes if the rule is still met.
• “I called” ends the alert until the rule is no longer met. If the rule is met again after that, the app alerts you again.

If you go back without choosing, the alert returns after 30 minutes at the earliest while the rule stays met. You can turn it off completely in the settings. The rule check and the alert are part of the free version of the app.

In the background the app can’t keep calculating. If interval and duration fit and only time is missing, it schedules a notification for the moment the period would be complete. It assumes your contractions keep coming in the same rhythm. When your contractions change, it schedules again.

Three examples, worked through with the app’s logic

These three sequences are made up and don’t come from users. We ran them through the same functions the app uses and evaluated them at 10:06 pm:

• Example A: 13 contractions from 9:00 to 10:04 pm, 5 to 6 minutes apart, each 50 to 70 seconds long
• Example B: 7 contractions from 9:34 to 10:04 pm, 4 to 6 minutes apart, each 50 to 65 seconds long
• Example C: 11 contractions from 9:00 pm, 5 to 6 minutes apart, each 55 to 65 seconds long. Between 9:32 and 9:48 pm there’s a 16-minute pause.

Result at 10:06 pm	Example A	Example B	Example C
Contractions in the last hour	12	7	9
Average interval	5:16 minutes	5:00 minutes	6:38 minutes
Average duration	59 seconds	59 seconds	61 seconds
Regular since	9:00 pm (66 minutes)	9:34 pm (32 minutes)	9:48 pm (18 minutes)
5-1-1	met, the alert comes	not yet, the hour is missing	not met
4-1-1	not met, interval too long	not met	not met

In example A all three conditions for 5-1-1 hold. At 5:16 minutes the interval is above five minutes but within the 30 seconds of slack. For 4-1-1 it would have to be 4:30 minutes or less. The contraction at 9:00 pm drops out of the averages and still counts for the run.

Example B fits on interval and duration, but the rhythm has only been regular for 32 minutes. Here the app schedules its notification for 10:34 pm.

In example C the pause ends the run, and the hour only counts from 9:48 pm. The 16 minutes also lift the average to 6:38 minutes. Before and after the pause, contractions came every 5 to 6 minutes.

We also worked through two variations of example A. If you tap only the start, 5-1-1 is still met, because the missing duration blocks nothing. If the same contractions last only 45 to 50 seconds, the average is just under 48 seconds. That’s below 54 seconds, so no alert comes.

Pattern detection and the phase hint

Besides the rule, there are two estimates that are part of the Premium version. Neither is a diagnosis.

Pattern detection looks at the last three hours and needs at least six contractions. It weighs five signals:

• Are the intervals getting shorter?
• Are the contractions getting longer?
• Is the rhythm steady?
• Are the contractions getting stronger? This only counts if you rate them.
• Do the contractions keep coming after you tapped “Lay down” or “Moved”?

For interval, duration and strength it compares the first half with the second. Each signal scores a point for, a point against, or nothing. If the points for lead by at least three and the rhythm is steady, the card says the contractions look like real labor. If the points against outweigh the points for, it says they look more like practice contractions. Otherwise it says “Not clear yet”.

Because pattern detection looks for change, it shows “Not clear yet” in example A although 5-1-1 is met. Interval and duration stay almost the same there. In example C the single long pause is enough for “more like practice contractions”. Only the rule decides whether the app tells you to call.

The phase hint places the last hour roughly by interval and duration:

• up to 3 minutes apart and at least 60 seconds long: may be transition
• up to 6 minutes and at least 45 seconds: active labor
• up to 10 minutes and at least 30 seconds: latent phase
• anything else, and any irregular rhythm: an early, still irregular phase

The app shows this hint from three contractions on, always with the sentence “Rough estimate from interval and duration, not a diagnosis. When in doubt, always call.”

Where 5-1-1 and 4-1-1 come from

The two presets follow rules of thumb that these sources describe:

• Lamaze International, a childbirth education organization, writes that many care providers tell parents to follow 5-1-1 or 4-1-1. That means contractions consistently 5 or 4 minutes apart, each lasting 1 minute, for at least an hour.
• familienplanung.de, a portal of Germany’s federal public health institute, describes the 5-1-1 pattern for a first baby. Contractions come regularly every five minutes for about an hour and last about a minute. The portal adds that the pain is so strong you can no longer distract yourself during a contraction. From the second baby on, the portal says it’s time once contractions come regularly every ten minutes.

The app only measures time. It can’t check how strong the pain is; that’s for you to judge. Lamaze suggests talking your plan over with your care provider.

Your own hospital’s or midwife’s advice always comes first. If they give you other numbers, for example for a second baby or a long drive, enter exactly those as a custom rule. How different hospitals set their numbers is covered in the 5-1-1 rule. What a single interval means is explained in contractions 5 minutes apart and other intervals.

What the app can’t do

• It doesn’t diagnose anything. It only knows the times and details you enter and examines nothing.
• It doesn’t notice when contractions stop. If you stop tapping, the time of the run keeps counting, and the alert can still come.
• It doesn’t check whether a contraction lasts longer than 2 minutes or whether 6 or more come in 10 minutes. The NHS names both as reasons to call urgently.
• It can’t tell that your water has broken, that you’re bleeding or that your baby is moving less. With signs like these you call right away, whatever the app shows. The full list is below this article.

The app needs no account and works offline. Your contractions stay on your phone.