If you are reading this, you are probably holding a screaming baby and wondering what went wrong. You just fed them. Changed them. Rocked them. Why are they fighting sleep?
The answer is likely Cortisol.
Most parents think, “If I keep the baby awake longer, they will be more tired and sleep better.” This is the single biggest myth in parenting. It is also completely false.
The Science of “Sleep Pressure”
Babies have a biological limit to how long they can stay happily awake. We call this the “Wake Window.”
• Newborns: 45-60 minutes
• 4-6 Months: 90 minutes
• 12 Months: 3-4 hours
Once your baby crosses that timeline, their brain dumps cortisol (the stress hormone) into their system. It’s a survival mechanism—like a shot of adrenaline. They get a “second wind,” but it’s a toxic one. They become wired, jerky, and impossible to settle.
The 90-Minute Rule
For babies between 4 and 6 months, the magic number is almost always 90 minutes.
If your baby wakes up at 7:00 AM, the clock starts ticking immediately. By 8:15 AM, you should be winding down (dim lights, white noise). By 8:30 AM, they should be asleep.
If you wait until 8:45 AM to start trying, you have missed the wave. You are now surfing in a cortisol storm.
How to Fix It Today
Stop guessing. Use the SleepyFormula Calculator on our homepage. It takes the guesswork out of the math. If the calculator says 9:00 AM, believe it. Put them down at 8:50 AM.
It might feel “too early.” Do it anyway. You will be shocked when they fall asleep without a fight.
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