How the Circadian Rhythm Planner calculates your schedule

This calculator uses your anchor time (wake time or bedtime) plus a few proven timing heuristics from sleep science to generate “windows” (not strict rules). The core idea is simple: your internal clock is trained mostly by light timing, consistent wake time, and how close stimulants and arousing activities occur to bedtime.

The planner starts by estimating your sleep opportunity window. If you enter a wake time, it computes: Bedtime = Wake time − Sleep hours. If you enter a bedtime, it computes: Wake time = Bedtime + Sleep hours. Times are wrapped across midnight automatically.

Next it applies a small chronotype adjustment. Early birds tend to prefer earlier bed/wake times, while night owls naturally drift later. To keep the planner practical, it uses a gentle shift: early bird = −30 minutes, night owl = +30 minutes for the “ideal” focus, nap, and wind‑down windows. (You can still follow the plan with your real schedule; the shift simply nudges the recommended windows.)

• Bright light exposure: within 0–30 minutes after wake for 10–30 minutes (outdoor light is best).
• Deep work peak: ~2–5 hours after wake (most people report strongest analytical focus here).
• Midday dip / nap: ~7–9 hours after wake (keep naps 10–20 minutes for minimal sleep inertia).
• Exercise window: ~4–10 hours after wake; avoid hard workouts in the last ~2–3 hours before bed.
• Caffeine cutoff: Bedtime − (6/8/10 hours) depending on sensitivity setting.
• Last big meal cutoff: ~3 hours before bed (helps reflux and temperature regulation).
• Dim‑light wind‑down: start ~2 hours before bed; aim for low light + calmer tasks.
• Screen “hard stop” (optional): ~60 minutes before bed; if you can’t, use warm/dim settings.

Why these offsets? They’re not magical — they’re behavioral guardrails. Light early supports alertness and advances your clock; bright light late delays it. Caffeine late can reduce sleep quality even if you fall asleep; intense exercise late can raise body temperature and adrenaline; heavy meals late can fragment sleep. When you align these levers, you create a “sleep‑friendly” day.

The result is a schedule designed to be realistic: you get a range for each activity, plus a short explanation so you understand what matters most (and what’s flexible). You can follow it on weekdays, then keep a narrower version on weekends to avoid “social jet lag”.

Example routines you can copy

These examples show what the planner outputs. Your exact times will vary based on your inputs.

• Bedtime: 11:00 PM
• Morning light: 6:30–7:00 AM
• Deep work: 8:30–11:30 AM
• Workout: 10:30 AM–3:30 PM
• Nap window: 1:30–2:30 PM (10–20 minutes)
• Caffeine cutoff: 3:00 PM
• Wind‑down: 9:00–11:00 PM

• Wake time: 7:30 AM
• Morning light: 7:30–8:00 AM
• Deep work: 10:00 AM–1:00 PM
• Caffeine cutoff: 4:30 PM (8 hours before bed)
• Wind‑down: 10:30 PM–12:30 AM

If you can only do one thing: keep your wake time consistent and get bright outdoor light early. Everything else becomes easier when those two are stable.

Understanding your circadian rhythm (in plain English)

Think of circadian rhythm as your body’s built‑in scheduling system. It helps coordinate sleepiness and alertness, body temperature, hunger hormones, and mental performance across the day. When your rhythm is aligned, you feel naturally sleepy at night and naturally alert in the morning. When it’s misaligned, you get that “tired but wired” feeling, late‑night scrolling, and morning grogginess.

The most powerful signal for circadian timing is light. Bright light soon after you wake tells your brain “it’s daytime”, which nudges your internal clock earlier (helpful if you want to fall asleep earlier). Bright light late at night tells your brain “it’s still daytime”, which can delay sleep. That’s why the planner puts light exposure early and a dim‑light wind‑down before bed.

The second most powerful lever is consistency. If you wake at 6:30 AM on weekdays but 10:30 AM on weekends, your body clock constantly re‑adjusts — like flying to a new time zone every Friday night. The planner doesn’t demand perfection; it encourages a wake time you can stick to most days and gives you a wind‑down routine that matches.

Then come the “supporting actors”: caffeine timing, exercise timing, meals, naps, and mental arousal. Caffeine has a long tail; even if it doesn’t keep you awake, it can reduce deep sleep. Exercise is great for sleep quality, but hard workouts too close to bed can push your nervous system into “on” mode. Heavy meals late can disrupt comfort and sleep. Short naps can rescue afternoon energy, but long naps or late naps can steal sleep pressure from the night.

The goal isn’t a perfect schedule. The goal is a schedule that makes the healthy choice the easy choice — with built‑in windows that fit real life.

Frequently Asked Questions

• Is this a medical circadian diagnosis tool?

  No. This is a practical planning calculator. It does not diagnose circadian rhythm disorders or sleep conditions. If you suspect a disorder, consider a sleep specialist.

• Should I plan from wake time or bedtime?

  Wake time is usually the strongest “anchor” because it’s easier to control. If you wake consistently, bedtime tends to follow. Use bedtime mode only if bedtime is already fixed (for example, you have a strict early start).

• What if I work night shift?

  Night shift flips the light rules. You’d want bright light during your “work day” and strict darkness before your “sleep day.” This planner is designed for standard day schedules, but you can still use it by treating your wake time as the time you wake up for work, even if that’s 5 PM.

• Do I have to stop caffeine 8 hours before bed?

  Not everyone, but it’s a strong default. Some people can drink coffee later with minimal impact; others are very sensitive. Use 6 hours if you sleep great, 10 hours if you’re struggling, anxious at night, or you’re actively trying to shift earlier.

• What’s the “best” nap length?

  For most people: 10–20 minutes. That’s long enough to refresh but short enough to avoid deep sleep grogginess. If you need a longer nap, keep it earlier in the day and expect a little sleep inertia.

• Why does morning light matter more than evening light?

  Both matter, but morning light is a clean signal that helps align your clock. Evening light is often accidental (screens, bright rooms). A little morning light plus a dim‑light wind‑down is a powerful combination.

• How fast can I shift my body clock?

  Small shifts add up. Many people can move their schedule by 15–30 minutes every few days. The fastest sustainable approach is earlier light, consistent wake time, and an earlier caffeine cutoff.