Eighteen months is the age when the whole day rests on a single nap and the evening turns into a negotiation for the first time. Your child says “no”, tests every boundary and can climb out of the cot. Below are the numbers the app itself works with — and an honest line between what has been measured and what is simply repeated.
Every figure below comes from the app's age table — the same one your child's plan is built from.
| Metric | Value | What it means |
|---|---|---|
| Daily sleep — target | 12 h 30 min | The goal the plan aims at |
| Night sleep — target | 11 hours | From falling asleep to the morning wake-up |
| Daytime sleep — target | 1 h 30 min | The single nap |
| Number of naps | 1 | Both the minimum and the maximum for this age |
| Wake window | 4–6 hours | From waking to the next time you settle them |
| Bedtime | 20:00 | The recommendation; 18:00–22:00 available in settings |
| “Morning” starts at | 05:00 | Earlier counts as an early wake-up |
| Night feeds | 0 | What the table expects, not a demand on the child |
| The app calls it a shortfall | under 10 h 15 min a day or 8 h 5 min at night | The lower edge of the healthy-child distribution |
This is the main difference between eighteen months and one year. The app measures the window from waking to the next settling and holds a 4–6 hour range with a 30-minute tolerance either side. In practice:
Note the width: two hours between the bottom and the top of the range is the largest spread of the first two years (at 9–14 months it was twice as narrow: 3–4 hours, that is sixty minutes against a hundred and twenty). That is not sloppiness in the table but a property of the age: at eighteen months children differ in stamina far more than at six. So one “correct” number does not work here — watching your own child does. The full account of the tool itself is in wake windows by age, and the cost of erring on the long side is in overtiredness.
From 15 months up to and including 18, the app's age table allows exactly one nap: minimum and maximum are both one. In other words, the model already treats the two-to-one transition as complete, and it builds the plan around a single nap.
One small practical consequence is easy to miss. By this age the app no longer shows the advice “a switch from two naps to one is possible” — that advice lives earlier, where the table still allows two naps. If you were waiting for a reminder about the transition and never got one, nothing is broken: by the app's reckoning the transition is behind you.
The series is not strictly decreasing, though, and that is worth knowing. At 19–23 months the ceiling rises back to two naps — not because children go back to two, but as an allowance for those who have not switched yet. The mechanics of the transition itself are covered separately in the two-to-one nap transition.
At eighteen months a refused nap is the most frightening thing of all: it feels as though the child is outgrowing it and the day is about to fall apart. The app disagrees, and quite firmly.
It does not consider dropping the nap as a possible transition before 30 months at all, and it only concludes “there are no naps any more, and that is fine” from 36 months. Before those ages the rule simply does not switch on — not “stays quiet out of caution”, but has no subject matter. At eighteen months a missed nap is an event of the day, not a stage of development.
What usually lies behind it: a morning window that was too short (settled less than 3 hours 30 minutes after waking — the tiredness is not there yet), a late wake-up, a trip, noise, visitors, a tooth coming through. A separate common trap is “catching up in the evening”: a short nap at five or six in the afternoon releases the built-up sleep pressure and pushes falling asleep later. It is more reliable to move bedtime closer to 19:00 — one evening with an early bedtime does not break the schedule.
This is the day the app itself draws on an empty diary with bedtime at 20:00. It is not a timetable to live up to but an illustration of the arithmetic.
| Time | What happens |
|---|---|
| 07:00 | Wake-up, breakfast, an active morning |
| 12:25–14:35 | The single nap (window 5 h 25 min) |
| 19:30 | The bedtime routine starts (window 5 h 25 min) |
| 20:00 | Bedtime |
| 20:00–07:00 | Night, 11 hours |
Both windows here are 5 hours 25 minutes — inside the 4–6 hour range, towards its upper end. The sleep in this example adds up to 13 hours 10 minutes, slightly more than the 12 hour 30 minute target: the nap in it is taken from the average for the age (2 hours 10 minutes) rather than from the plan's target (1 hour 30 minutes). That is exactly the case described above: different quantities behind one word, and both of them legitimate.
Parents usually use “the 18-month crisis” for several things at once: protest at bedtime, evening negotiations, night-time calls, the demand to do everything unaided. The phenomenon is recognisable, and there is no point denying it. But it has neither a measured duration nor a measured cause — and this article is not going to promise either.
One thing at eighteen months genuinely has been measured, and it deserves a place of its own — night terrors. See below.
Your child has discovered the word “no” and is trying it where it works best — on the boundary of the day. This is the development of autonomy, not a spoiled character. What helps: a very simple, always identical sequence of steps (one book, a hug, sleep) and choice inside your frame rather than instead of it — “this book or that one”, but never “sleep or no sleep”. Bedtime itself is not up for discussion: it stays the same. A ready-made evening script is in the bedtime routine.
It looks like this: in the first hours after falling asleep the child screams and thrashes without waking; comforting does not help and sometimes makes the episode worse; in the morning they remember nothing. This is not a nightmare — a nightmare comes in the second half of the night, and the child wakes and can be comforted. In a survey of the mothers of 1940 children, the prevalence of night terrors peaks at exactly eighteen months: 34.4% (95% confidence interval 32.3–36.5) — Petit 2015. What to do: do not wake them, move anything dangerous out of the way and wait for the episode to end. This is precisely what the app shows to parents of children aged 18–23 months as a separate note. What it does not do is claim that your child is having night terrors: such an episode is simply invisible in sleep-time records.
The skill appears at roughly the same time, and it is about safety, not the schedule. Lower the cot base to its lowest position and take away anything that can be stood on. If that does not help, a low bed is safer than leaving a child to climb over the rail. Return them to bed silently and identically every time: the conversation at that moment is the very reward worth getting up for again.
The app's age table expects zero night feeds at this age — but that is the continuation of a falling series, not a measurement: its sources hold no direct data beyond 12 months. The waking itself does not disappear; what changes is how it ends. If wakings repeat night after night, the reason is usually not the age but the way of falling asleep — the causes are set out in frequent night wakings. One technical detail for later: a gap shorter than 20 minutes is counted by the app as part of the same night rather than two separate sleeps (at one year that threshold was 25 minutes, below one year 30).
A wake-up before 5 a.m. counts as early and the app says so straight away. About a persistent early wake-up it speaks more cautiously: it needs at least 10 nights recorded in a two-week window, with at least 5 of them starting before five. The commonest causes at eighteen months are a last window that ran too long the day before, and light in the room: in summer dawn comes long before the wake-up, and that alone is often enough. There is a separate account in early waking, and on darkness and quiet in the sleep environment.
Different conclusions switch on at different depths of the diary:
Before that the app is not silent; it simply talks about the age rather than about your child. On the nap transition specifically: the app is ready to spot it from 8 months up to and including 23, but it only says anything when a two-week window holds at least 10 days with records and, within them, at least 5 days with one nap and at least 5 with two. At eighteen months such a mix is rare: for most children all the days already look the same.
And one more thing: days marked “ill” or “teething” are excluded from learning, and the wake window range on such a day widens by 30% in both directions — how that works.
Not everything is solved by the schedule. See your paediatrician without delay if:
This is not a list of diagnoses and not a reason to make one yourself. Neither this article nor the app can recognise an illness from sleep records.
The app aims at 12 hours 30 minutes a day: 11 hours at night and an hour and a half in the daytime. That is a target for the plan, not a yardstick for judging a child. It only speaks of a shortfall if the daily total drops below 10 hours 15 minutes or the night below 8 hours 5 minutes.
One. From 15 months up to and including 18, the app's age table allows exactly one nap, and the plan is built around it. At 19–23 months the ceiling rises back to two — that is an allowance for children who have not yet made the switch, not an expectation of returning to two naps.
Between 4 and 6 hours, with a 30-minute tolerance. Under 3 hours 30 minutes the app says “not tired yet”; over 6 hours 30 minutes it says “overtired”. This is the widest range of the first two years: a band two hours wide, with one child's day sitting in its lower half and another's in its upper half.
At eighteen months, almost certainly not. The app does not even consider dropping the nap as a possible transition before 30 months, and it only concludes “there are no naps any more, and that is fine” from 36 months. Before that, one-off refusals usually come down to a morning window that was too short, a late wake-up or the events of the day. What helps: keep the time of the nap and offer quiet rest in a darkened room even when sleep does not happen.
It is a parents' word, not a measured quantity. We could not find a study showing a spike of sleep problems at exactly this age or naming its duration, so there are no calendar promises here. What is genuinely measured at this age is night terrors: in a survey of the mothers of 1940 children their prevalence peaks at eighteen months at 34.4% (Petit 2015). The app itself claims nothing of the sort about your child: it does not name a cause from sleep records.
The app's age table expects zero — but that is the continuation of a falling series, not a measurement: its sources contain no direct data on night feeds beyond 12 months. Whether a particular child needs them, and when to drop them, is a question for your paediatrician: it is about nutrition and growth, not only about the schedule.
Baby Sleep Planner works out wake windows and settling times from your child's age and their own records, not from an averaged table off the internet.
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