How long does it take to learn my baby's rhythm?

With two or three days of records, what your baby does already counts for more than the table for their age. At around eight useful windows the confidence is full, and the app tells you the percentage at every moment.

And if they skip a nap one day?

It does not matter. Recent counts for more, but an odd day gets diluted: the average is exponential with a half-life of five days, and anything far outside the reference is dropped.

Wake windows by age: how long a baby stays awake

A wake window is the stretch a baby stays awake between one sleep and the next. It is the number everything else comes out of: know it and you know what time the next nap is due without guessing.

The table, and what it is actually for

Windows grow with age: around 50 minutes for a newborn, an hour and a quarter at three months, two hours at six, close to three at a year. Those numbers are an honest starting point and nothing more.

The trouble with using them as the answer is that the range of normal at any age is enormous. Two five-month-olds can last an hour and a half and two and a half hours, and both are fine. An app that hands you the number from the table gets the average right and gets your child wrong.

A window is not worth the same at any hour

The first of the day, the one after the night, is the shortest: they wake up rested and sleep comes back round sooner. The last one, before bed, is the longest.

This matters when you do the sums: averaging every window of the day into one number makes the first nap come out late every time and the last one early every time. napnap normalises each observation by the slot it fell in before averaging it, and applies the factor for the slot in question again when it predicts.

And a short nap shortens the next one

After a twenty-minute nap they do not last as long as they do after an hour and a half. It is something you see for yourself at home and almost no app picks up.

It is not proportional: sleeping half as long does not leave a baby with half the wind in them, it leaves them with a little less. napnap carries part of the difference across, capped at both ends, so that one odd nap in the car does not rewrite the whole afternoon.

What makes a window count

A five-minute doze in the pram says nothing about how long they stay awake. Counting it muddies the average and makes the times move for no reason.

napnap only learns from windows that ended in a sleep of twenty minutes or more. And a nap that stopped at a single cycle —under 45 minutes— does not count as a window well judged: it does not say the sum was right, it says it was cut where naps get cut.

Questions

How long does it take to learn my baby's rhythm?: With two or three days of records, what your baby does already counts for more than the table for their age. At around eight useful windows the confidence is full, and the app tells you the percentage at every moment.
And if they skip a nap one day?: It does not matter. Recent counts for more, but an odd day gets diluted: the average is exponential with a half-life of five days, and anything far outside the reference is dropped.