Sleep comes in ~90-minute cycles — waking up mid-cycle is what makes you feel groggy. Pick a wake-up or bedtime and see the times that land you between cycles.
Assumes ~14 minutes to fall asleep, then full 90-minute cycles. 5-6 cycles (7.5-9 hours) is the range most adults land in.
Free, unlimited, no account. If this saved you a paid tool, a small thanks is appreciated.
Say thanks — $3