Smartwatches can estimate how well you feel you slept, not just how long you slept, by comparing each night with your own normal and adding a few facts about you.
the5krunner’s take: It sounds superficially crazy. Why have a watch telling you how you feel? Watch makers should build this, because a sleep score that agrees with how wearers feel is the cheapest way to make them believe every other number on the watch.
- The finding draws on three years of data from 4,794 people in Israel who wore a smartwatch and rated each night’s sleep from awful to excellent, giving 759,116 ratings and 1.77 million days of watch data. It was published on 10 November 2026.
- A machine learning model correctly distinguished nights rated awful from nights rated excellent most of the time, scoring 0.88 out of 1. Telling an ordinary poor night from an ordinary good one was harder, at 0.76.
- Nights rated awful came with about an hour less sleep, 10 more minutes awake, and roughly one extra waking from dream sleep every two nights. The day before had about 750 fewer steps and more stress.
- The strongest single clue was sleep length compared with that person’s own last 90 days, not the raw number of hours.
- Watch data alone and personal details alone each did a modest job, and together they did much better. The most useful personal detail was how well someone said they usually slept.
- No new sensor is needed. Everything used is already measured by mainstream watches.
For wearable makers: a sleep score people agree with buys trust in the rest
Sleep is the one metric every wearer can quickly check against their own experience each morning, and today’s scores regularly fail that check, showing 85 after a night the wearer knows was rough. Judging each night against the wearer’s own normal, adding the day before and asking a few questions at setup fixes much of that without new hardware. For wearers, the gain isn’t being told how they feel, but a record of the nights they forget, the run of bad weeks they shrug off, and the day-before habits that preceded them. Passed-on trust is worth most to Garmin, whose second tier of sporty metrics, such as Training Readiness, Training Status, Body Battery and the race predictor, sits on sleep and recovery data that owners cannot check for themselves.
Quick answers
Why does my sleep score not match how I feel?
Most scores compare you with general averages and look only at the night. How rested you feel depends more on how the night compares with your own normal and on the day before.
Can a smartwatch tell if I slept badly?
It can estimate it. Watch data plus a few personal details picked out awful nights from excellent ones most of the time, but was less reliable between ordinary nights, so it suits spotting a bad patch rather than judging one morning.
Related: InnerRipple tells Apple Watch owners what’s normal for them and is Wahoo’s Oura readiness the best approach?
Source and original research by: the5krunner and Communications Medicine.
If you enjoyed this quick read, here are three more in the series:
- Huawei Sense G1 – Continuous Blood Glucose (Invasive)
- Runna caps seven-day plans to cut injuries
- Peloton borrows $700m as junk, at 8.63%
Last Updated on 14 November 2026 by tfk the5krunner
Small things I always use
- Garmin 90-degree charging adapter: Charges your Garmin with any USB-C cable. Essential when travelling. I use one.
- Body Glide: The blue anti-chafing stick swimmers and runners carry. I use it.
- Speedo earplugs: Fewer ear infections and no cold-water dizziness. I use them.
- Dryrobe Advance: My winter changing robe for open-water swims. I use one. A cheaper option is the AONYIYI changing robe.
- Maurten: Race fuel that stays easy on the stomach. I use them.
- Beet It Sport nitrate shots: Beetroot shots I take in the days before a race. I use them.
- Garmin charging puck: The quickest way to top up before a session. I use one.
- Injinji: Toe socks that stop rubbing, so you run more. I use them.
- Ultimate toe protectors: Stop black toenails on long runs. They work. I use them.
- Compressport R2 v2 calf sleeves: My calf sleeves of choice. I use them.
- Cellucor C4: My pre-workout before hard sessions.
- TPU tubes: Schwalbe Aerothan, Tubolito and Pirelli SmarTube. Light, tiny spares. I use all three.
- G8 insoles: Adjustable arches, perfect position. I use them.
- Cycplus Cube: A 97g electric pump that gets a road tyre rideable in two minutes. I carry one. 5% off with code THE5KRUNNER.
Health, recovery and sleep
- Kineon MOVE+: Red and infrared light for sore knees, Achilles and other joints after hard training. I use it.
- FreeStyle Libre 3 Plus: Shows how my blood sugar responds to diet. Occasional use.
- hDrop: Measures my sweat loss in summer and indoors. I use it.
- Fourth Frontier Zone: Checks my heart under load in hard sessions.
- Oura Ring 5: My partner’s recovery tracker of choice.
- Eight Sleep: A cooling mattress cover my partner and I use nightly.
Watches and sensors
- Polar H10: My daily driver for waking HRV.
- Polar Verity Sense: My backup arm-worn HR sensor.
- Nomad bedside charger: Charges my iPhone and Apple Watch overnight. I use it, and many of their bands.
- Train.Red: The best muscle oxygen sensor I’ve used. Occasional use.
- Tymewear: Accurate heart rate and reliable ventilatory zones. I use it to pace endurance rides over an hour.
- Garmin Forerunner 970: A pro-grade triathlon watch. I use this.
- Apple Watch Ultra 4: My daily smartwatch. No phone needed on rides.
On the bike
- Continental GP5000 for everyday riding, and Aero 111 on the front for special occasions. I use both.
- Helmets: Specialized S-Works Evade 3 for road riding, and Rudy Project Wing for TT-style races. I use both.
- Ravemen FR300: A front light that mounts under your Garmin or Wahoo. I use one.
- Ravemen FR1000: The light and the computer mount in one unit, so nothing else goes on the bars. Better than mine.
- Ravemen FR1500SE: 1,500 lumens hanging under your Garmin, for proper night rides.
- Ravemen FR1100SE: 1,100 lumens under your Garmin, and up to 46 hours on slow flash.
- Ravemen FR500: A brighter FR300 with the same mount.
- Wahoo TRACKR Radar: I use it on one bike and Varia on the other. They perform the same.
- Garmin Varia RTL515: Radar that warns you of cars from behind. I use this model.
- Wahoo ELEMNT Roam 3: The bike computer that’s easy to use. I use mine on most rides.
- Favero Assioma Pro RS2: Accurate power pedals that swap easily between bikes. I use this model.
Home and indoor training
- NPE Runn: Makes my basic treadmill smart, sending more accurate speed and distance to my watch and Zwift. I use it.
- Google Wifi: Keeps Zwift connected in my pain cave. I use it.
- Apple TV 4K: Zwift on the big screen. I use two.
- Google Nest Doorbell (wired, 2nd gen): My video doorbell, running in both Google Home and Apple Home via Starling. I use it.
Reader-Powered Content
This content is not sponsored. It’s mostly me behind the labour of love, which is this site, and I appreciate everyone who supports it.
Support the site: Follow (free, fewer ads) · Subscribe (paid, ad-free) · Buy Me A Coffee
Written by real people, with AI assistance. Fact-checked and verified for originality. See the Editorial Policy. FTC: Affiliate Disclosure — some links pay commission. As an Amazon Associate, I earn from qualifying purchases.
tfk is the founder and author of the5krunner, an independent endurance sports technology publication. With 20 years of hands-on testing of GPS watches and wearables, and competing in triathlons at an international age-group level, tfk provides in-depth expert analysis of fitness technology for serious athletes and endurance sport competitors. See the gear tfk uses. ID
