Sleep Calculator: What Time Should I Go to Bed?
Tell us when you need to wake up and we'll work out the best times to go to bed — timed to 90-minute sleep cycles so you wake at the end of a cycle feeling refreshed, not groggy. It takes about 15 minutes to fall asleep, and we've built that in.
Written by Seán — Lead Reviewer, MattressReviews.ie
Testing team: Aoife (Side Sleeper Specialist), Ciarán (Back Sleeper Specialist), Siobhán (Combination Sleeper Specialist) & Oisín (Stomach Sleeper Specialist)
3+ years testing mattresses for Irish consumers. How we test · Meet the team
Go to bed at one of these times:
9:45 PM
9 hrs · 6 cycles
11:15 PM
7.5 hrs · 5 cycles
12:45 AM
6 hrs · 4 cycles
2:15 AM
4.5 hrs · 3 cycles
Based on 90-minute cycles + 15 minutes to fall asleep. Highlighted times give most adults 7.5–9 hours.
Working back from an Irish morning: most primary and secondary schools start between 8:40 and 9:00 AM, and a standard 9-to-5 office day means leaving the house around 8:00 AM. If you need to be up at 6:30 AM, a 9:46 PM or 11:16 PM bedtime keeps you on full cycles.
A note on health advice: This guide is for general information only and is not medical advice. Sleep problems can have many causes. If poor sleep is affecting your daily life, lasts more than a few weeks, or you suspect a condition such as insomnia or sleep apnoea, speak to your GP. In Ireland you can also find guidance at HSE.ie.
How do sleep cycles work?
Sleep isn't one long, flat state — you move through repeating cycles, each lasting roughly 90 minutes. A single cycle takes you down through light sleep, into deep (slow-wave) sleep where the body repairs itself, and back up into REM sleep, where you dream and consolidate memories.
Over a full night you'll complete four to six of these cycles. Earlier cycles are heavier on deep sleep; later ones contain more REM, which is why the last few hours of sleep are so important for mood and memory — and why cutting your night short hits harder than the lost hours suggest.
The grogginess you feel some mornings is sleep inertia: your alarm has dragged you out of deep sleep mid-cycle. Waking at the end of a cycle, when you're already in lighter sleep, feels far easier — and that's exactly what the calculator above aims for.
Why 90 minutes?
Ninety minutes is the widely-used average length of one adult sleep cycle. It's a planning figure, not a stopwatch: real cycles range from about 70 to 120 minutes, tend to be shorter early in the night, and stretch out towards morning. Individual factors — age, caffeine, alcohol, stress and sleep debt — all nudge it.
That's why this is a calculator, not a guarantee. Treat the suggested times as a strong starting point, then adjust by 15–20 minutes either way depending on how you actually feel when you wake. After a week or two you'll learn which option suits you.
How much sleep do you actually need?
Cycle timing only helps once you're getting enough total sleep. These are the ranges recommended for each age group by the US National Sleep Foundation — figures echoed by the HSE for Irish families.
| Age group | Recommended sleep (per day) |
|---|---|
| Newborns (0–3 months) | 14–17 hours |
| Infants (4–12 months) | 12–16 hours |
| Toddlers (1–2 years) | 11–14 hours |
| Pre-schoolers (3–5 years) | 10–13 hours |
| Children (6–12 years) | 9–12 hours |
| Teenagers (13–18 years) | 8–10 hours |
| Adults (18–64 years) | 7–9 hours |
| Older adults (65+) | 7–8 hours |
Want the full breakdown by life stage, including why teenagers' body clocks run late? See our guide to how much sleep you need by age. And getting your bedroom temperature right is one of the easiest ways to protect those hours.
How to fall asleep faster
The calculator assumes 15 minutes to drift off. If you're regularly lying awake far longer, these evidence-backed habits help shorten it:
Keep a consistent schedule
Going to bed and waking at the same times every day — yes, weekends too — is the single most effective way to fall asleep faster. It anchors your body clock so sleepiness arrives on cue.
Cool the room down
Your core temperature needs to drop to trigger sleep. A bedroom around 16–18°C helps; an overheated Irish bedroom with the heating left on overnight fights against it.
Dim screens an hour before bed
Bright and blue-rich light from phones and TVs suppresses melatonin, the hormone that signals sleep. Switch to dim, warm lighting in the last hour and put the phone out of reach.
Mind caffeine and alcohol
Caffeine can linger for 6+ hours, so keep that afternoon coffee before 2–3 PM. Alcohol may help you nod off but fragments the second half of the night, costing you valuable REM sleep.
Get the bed itself right
A sagging or too-firm mattress and the wrong pillow keep you shifting and surfacing. Comfortable, well-supported sleep makes falling asleep almost automatic.
Is your mattress part of the problem?
Perfect bedtimes won't help if you're surfacing every cycle on a worn-out or unsuitable mattress. Our 2-minute quiz matches you to the right type, firmness and size for how you sleep — no email required.
Take the 2-minute mattress quiz →Frequently Asked Questions
Keep reading
- → Bedroom temperature for better sleep — the easiest environmental fix for falling asleep faster.
- → Best cooling mattresses in Ireland — if you wake up hot mid-cycle.
- → Take the mattress quiz — find the right mattress for how you sleep.