Nightly shortfall
The gap between how much your body needed and what it actually got. Quality counts — a fragmented night doesn't fully cancel a deficit.
Sleep Debt Tracker · 7-day rolling deficit
The sleep debt
your body keeps.
One bad night isn't a debt. Seven days of them is. Body Insights reads what your Apple Watch already recorded and translates the rolling cost — in plain language, not a number you have to interpret.
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Free for core features.
"I slept eight hours. Why am I still wrecked?"
Because the body doesn't keep score one night at a time.
You can have a single rough night and recover by lunchtime. You can also string four merely-okay nights together and find yourself, on a Friday afternoon, unable to remember why you walked into the kitchen. The first is a blip. The second is sleep debt — and most sleep apps will tell you you're doing fine, because they only read last night.
Sleep debt is what your body is carrying across days. Body Insights reads your Apple Watch sleep records on a 7-day rolling window and translates the rolling deficit into the only thing that matters in the morning: "This week is catching up with you. Today, take it slow."
One night is weather. A week is climate.
Last night might have been short. The thermometer on the right is what your body is actually carrying into today.
A single rough night isn't debt. The rolling window is — and it's what the body is actually carrying into the next day.
Why a rolling window — and not last night.
Sleep restriction is one of the most-studied stressors in human physiology, and the consistent finding is this: the cost compounds. A landmark paper by Van Dongen and colleagues found people who slept six hours a night for two weeks showed cognitive impairments comparable to staying awake for forty-eight hours straight — and most of them rated themselves as "only a little tired." The body kept the receipt; subjective awareness didn't.
That's why a single-night view is misleading. You can sleep eight hours and still be running on the previous four nights. A rolling window — seven days, the standard in the research — is the shortest unit that captures how the deficit is actually felt.
Body Insights reads your sleep records on this scale by default. The shape of the week is the signal.
The part nobody likes to say out loud.
A line of research stretching back decades — Dawson and Reid in Nature (1997), Williamson and Feyer in Occupational and Environmental Medicine (2000), and many others since — has compared sustained sleep deficits to blood-alcohol-equivalent impairment on reaction-time and judgment tasks.
The headline ("being chronically underslept is like being legally drunk") is a real finding, but it's a careful one. The exact equivalence depends on the task, the person, and how the deprivation was structured. The honest version is gentler and harder to dismiss: after a week of sustained deficit, your reaction time and judgment measurably degrade in ways that look, on lab tests, similar to mild intoxication.
We don't publish a number alongside your week. The point isn't a score — it's that the cost is real, and your body is the one paying it.
An honest note on recovery.
Sleep debt isn't a credit card. A long recovery night helps — measurably — but the research is clear that some of the cost of sustained sleep restriction doesn't get cleared by a weekend lie-in. Metabolic markers, insulin sensitivity, and some aspects of cognitive performance lag past the moment you feel rested again.
So we won't tell you the debt has been "erased." We'll tell you the rolling window is lighter than it was. We'll tell you which direction it's trending. We'll tell you, gently, when the pattern says: this isn't a one-night fix. The recommendation that follows is usually about pacing — not pushing harder, not trying to bank the perfect night, but stopping the slow add.
See what your week is carrying
Free for core features. No card needed.
For people who want the science.
Everything below is what an honest sleep debt tracker should tell you. If you're shopping comparisons, you're in the right place.
What we read, and how we read it.
The sleep debt tracker reads sleep data from Apple Health — the same records your Apple Watch already writes there overnight. Your Apple Watch tracks. We translate.
7-day rolling sum
The standard research window. Long enough to see a pattern, short enough that recent nights still matter.
Recovery sensitivity
A long, deep night reduces the rolling load. The pattern softens; we don't claim it disappears.
Trend direction
Whether the rolling deficit is climbing across weeks, easing back, or holding steady — qualitative, not a percentage.
Personal baseline
Sleep need varies. After two weeks of your data, we learn yours rather than assuming the textbook number.
Plain-language morning
One sentence that ties the week to today: "More in the bank than you thought" or "This week is catching up with you."
Is sleep deprivation really like being drunk?
The short version: yes, in a careful sense.
Dawson and Reid (Nature, 1997) ran controlled trials comparing extended wakefulness to measured blood-alcohol levels and reported decrements on reaction-time tasks that matched mild intoxication after roughly 17–24 hours awake. Williamson and Feyer (Occupational and Environmental Medicine, 2000) extended the finding to performance batteries used in occupational safety. Subsequent work has refined and qualified the comparison — the exact equivalence varies by the task, the type of deprivation (acute total vs. chronic partial), and the individual.
What's robust across all of it: sustained sleep deficits measurably impair reaction time and judgment. The most popular framing ("a week of six-hour nights equals being legally drunk") oversells a specific number. The underlying finding doesn't need the oversell.
Sleep debt tracker vs Whoop, Oura, and the built-in apps.
If you've tried the others and they didn't fit, here's where we differ.
| Apple Sleep | Whoop / Oura | Body Insights | |
|---|---|---|---|
| Last-night view | Yes | Yes | Yes |
| 7-day rolling debt | No | Partial | Yes |
| Honest about recovery limits | N/A | No | Yes |
| Plain-language morning | No | Partial | Yes |
| Tuned for variable energy | No | No | Yes |
| Subscription | None | $6–30 / month | Free for core |
| Extra hardware | None | Ring or strap | None |
Whoop and Oura built careful products — for athletes pushing strain into recovery. If your week doesn't follow a training cycle, you'll find the framing here closer to fit.
Questions you're probably asking.
What is sleep debt, really?
The rolling shortfall between the sleep your body needed and what it actually got. One bad night isn't debt. A week of them is — and it's what the body is carrying into today.
Why 7 days?
It's the standard research window for measuring the cumulative cost. Long enough to show a pattern, short enough that this week still matters more than last month.
Can I erase sleep debt with a long weekend?
Partly. A long recovery night lightens the rolling load. Research suggests some cognitive and metabolic effects linger past what a lie-in repairs. We don't promise to undo it — we surface it so you stop adding to it.
Is it really like being drunk?
The findings from Dawson and Reid (1997) and Williamson and Feyer (2000) compare sustained deficits to mild intoxication on reaction-time tasks. The exact equivalence varies — the underlying impairment is real.
Do I need a CGM?
Not for sleep debt. It reads what your Apple Watch already records. CGM data enriches other parts of the app, not this one.
How much does it cost?
Free for core sleep debt features. A premium tier adds deeper personalization. No card needed to start.
Your sleep data stays yours.
On-device. No account. No subscription required. No data sold. Ever.
- Reads from Apple Health
- Stays on your iPhone
- You choose what to share
See what your week is carrying.
Free for core sleep debt features. Premium adds deeper personalization.
