Baby Bedtime Calculator

Of all the numbers in baby sleep, the last wake window matters most. It is the stretch of awake time between the final nap and bedtime — and it controls how much sleep pressure your baby carries into the night. Too short, and they are not tired enough to fall asleep easily. Too long, and overtiredness floods them with cortisol, which causes bedtime battles and more night wakings.

How to use the last wake window

Note when the last nap ends (not when it starts), then add one full wake window for your baby's age. A 6-month-old whose nap ends at 4:00 PM with a 2–2.5 hour window is ready for bed between 6:00 and 6:30 PM. Start the wind-down routine — bath, books, dim lights — about 20–30 minutes before the target time so they are drowsy, not wired, when you put them down.

When the day goes off script

• Skipped the last nap? Do not hold bedtime. Move it earlier by roughly one wake window to avoid overtiredness.
• Last nap ran very late? You can cap it — gently waking a baby from a late nap protects bedtime more than it disrupts the nap.
• Short last nap? Treat the next wake window as starting from when they woke, and offer bedtime a little early.

Watch the baby, not just the clock

Wake windows are averages. Yawning, eye rubbing, zoning out, and fussiness are your baby's way of saying the window is closing. If sleepy cues show up well before the window ends — during regressions, growth spurts, or illness — trust the cues and go early. Consistency in the routine matters more than hitting an exact minute.

Bedtime battles usually mean one of two things

If your baby plays happily in the crib for 45+ minutes, the last wake window was probably too short — try stretching it by 15 minutes. If they are wired, cranky, and fighting hard, it was probably too long — try 15 minutes earlier tomorrow. Adjust in small steps and give each change 3–4 days.