Fitbit vs Garmin: Fitbit Is the Steadier Record
What each one measures, how well that holds up in published studies, and where the two differ.
Fitbit and Garmin measure several of the same core signals through meaningfully different windows and philosophies, from resting heart rate timing to how each brand chooses to report, or deliberately not report, blood oxygen. Every section below compares what's actually measured and how strong the evidence behind it is, drawn from each brand's individually-verified metric pages. For depth beyond a single metric, the full Fitbit and Garmin profiles cover each device on its own.
Fitbit or Garmin: Which One to Buy?
For the steadier evidence record, Fitbit: it measures resting heart rate the same way across models and both brands now have an independent VO2 max test, and Garmin's method varies by model. Neither brand's blood oxygen reading has enough testing to choose on.
Price (US). Fitbit Air from $99.99 and Fitbit Edge from $179.99; Google Health Premium coaching is optional, from $9.99. Garmin sells many models at a one-time price; the core Garmin Connect app is free, and Garmin Connect+ is optional at $6.99 a month or $69.99 a year.
Which Measures Resting Heart Rate on a Wider Window?
Fitbit
Averages heart rate during non-movement periods across the full day, including daytime, rather than restricting the measurement to overnight.
Garmin
Reports the lowest 30-minute average heart rate recorded in the last 24 hours, a narrower, minimum-seeking window rather than a full-day average.
Where the evidence actually differs
These are different calculations, not just different labels: Fitbit averages across many low-movement moments through the day, Garmin specifically hunts for the single lowest 30-minute window in a rolling 24 hours. The same person could see meaningfully different resting heart rate numbers on the two devices simultaneously.
What published research found
Fitbit consistent, Garmin variesA 2022 evaluation of a Fitbit Charge 4 against a Holter ECG found its error stayed under 10 percent overall, best during seated rest and weakest during high-intensity intervals. Garmin's own independent evidence is less consistent across models: a Forerunner 235 had the weakest agreement of four wrist-worn monitors in one cardiac-rehab study, a Fenix 5 was similarly weak during variable-intensity trail running, but a Vivosmart HR+ and a Vivosmart 4 scored well in separate studies. Fitbit's evidence base is smaller but more uniform in what it shows; Garmin's is larger but split by which specific model was tested.
Full citation lists on each brand's own resting heart rate sectionsHead-to-head against an ECG. In the one study that has tested several consumer wearables against the same ECG reference at the same time, 13 healthy adults wore five devices overnight for a combined 536 nights. The Garmin model tested was the Fenix 6, which agreed poorly with the ECG for overnight HRV, with a concordance of 0.87 and an average error of 10.52 percent, and was left out of the resting heart rate analysis for methodological inconsistencies. Other Garmin models were not tested (Physiological Reports, 2025). No Fitbit device was in that study.
Which VO2 Max Estimate Has Stronger Independent Validation?
Fitbit
Cardio Fitness Score tracks the running pace-to-heart-rate relationship. A peer-reviewed validation of the Fitbit Charge 2 found it gave a consistent, unbiased read on relative fitness but overestimated actual lab-measured VO2 max, and that a simple age/resting-heart-rate/body-composition equation matched it for accuracy without requiring a run.
Garmin
Keeps the scientific "VO2 Max" label directly, estimated via the licensed Firstbeat Analytics algorithm during outdoor runs and walks. Garmin's own controlled validation reports roughly a 5 percent margin of error against lab spirometry, though independent testing using wrist-based optical heart rate rather than a chest strap reports larger errors.
Where the evidence actually differs
Both estimates are algorithm-derived, not lab-measured. Fitbit's has a specific, citable independent study behind it. Garmin's has three, all small. In a study of the Garmin Forerunner 265, the watch's VO2 max after 12 weeks of training read higher than the lab measurement, 45.00 against 42.43 ml/kg/min, and its half-marathon predictions were faster than the actual race times, 129.97 against 137.55 minutes, with average errors under 10 percent for both (Howard et al., Journal of Medical Engineering and Technology, 2026). In 19 adults the Fenix 6 erred by 7.05 percent with a concordance of 0.73 (Sensors, 2025), and in 24 adults the older Forerunner 920XT by 7.3 percent, reading low on average (International Journal of Environmental Research and Public Health, 2019).
Correction, 2026-10-15
This section previously said no independent study of Garmin's VO2 max estimate had been found. A 2026 independent study tested the Forerunner 265, and its result is now given.
Correction, 2026-10-25
This section then said Garmin's VO2 max had one independent study, and the evidence summary below still said none had been found. It has three, on the Forerunner 265, the Fenix 6 and the Forerunner 920XT, and both now say so.
What published research found
Both independently testedThe peer-reviewed Fitbit Charge 2 validation gave a consistent, unbiased read on relative fitness but overestimated lab-measured VO2 max, and found a simple age/resting-heart-rate/body-composition equation matched it for accuracy without requiring a run. Garmin's estimate has been tested on three models, each in one small study: the Forerunner 265 read higher than the lab after training, the Fenix 6 erred by 7.05 percent, and the Forerunner 920XT by 7.3 percent, reading low on average.
Freeberg et al., mHealth, 2019 (doi:10.21037/mhealth.2019.09.07) · Howard et al., Journal of Medical Engineering and Technology, 2026 (doi:10.1080/03091902.2026.2741912) · Carrier et al., Sensors, 2025 (doi:10.3390/s25010275) · Passler et al., International Journal of Environmental Research and Public Health, 2019 (doi:10.3390/ijerph16173037)How Differently Do the Two Brands Report Blood Oxygen?
Fitbit
Reports two separate things: an actual nightly-average "SpO2" percentage, and a separate "Estimated Oxygen Variation" relative overnight graph with a red, yellow, or green pattern flagging possible breathing disturbances.
Garmin
Pulse Ox reports an actual percentage, available as either an on-demand spot check or continuous all-day and overnight tracking depending on device settings.
Where the evidence actually differs
Both brands report an actual percentage now, a real change from when Fitbit's EOV graph looked like its only SpO2 feature. The remaining difference is measurement window and flexibility: Garmin can run on-demand or continuously depending on settings, Fitbit's SpO2 is sleep-derived only.
What published research found
Insufficient evidence, both brandsDedicated searches for independent validation of either brand's blood oxygen sensing against reference oximetry returned nothing device-specific for either one. The general pulse-oximetry literature documents real accuracy problems this feature would inherit regardless of brand, including skin-pigmentation bias and motion artifact, but whether either implementation handles those conditions well is unknown for both.
Absence determined by dedicated per-brand searches, 2026-09-18Does Garmin Have Anything Like Fitbit's ECG Feature?
Fitbit
Sense 2 offers AFib monitoring through an on-demand ECG app, similar in concept to Apple's, paired with a passive Irregular Heart Rhythm Notification using the same optical sensor as everyday heart rate tracking.
Garmin
An FDA-cleared on-demand single-lead ECG app since January 2023, but only on select models (epix Pro, fenix 7 Pro, Venu 3 series, tactix 7 AMOLED, Venu 2 Plus at launch; later fenix 8, Forerunner 970, Enduro 3, Venu 4), not across the current lineup the way Fitbit's ECG spans Sense 2, Sense, Charge 5, and Charge 6.
Correction, 2026-09-20
This section previously said Garmin had no widely-offered ECG feature, the same false claim already corrected on garmin.html this week. Garmin has had an FDA-cleared single-lead ECG app since January 2023, though on a narrower set of models than Fitbit's ECG coverage. Corrected to reflect that both brands have a real ECG feature, differing in device breadth rather than existence.
Where the evidence actually differs
Both brands have a real, FDA-relevant ECG feature; the gap is device breadth, not a binary have/don't-have split. Garmin's own FDA submission data (86.5 percent sensitivity, 91.1 percent specificity) is vendor-submitted rather than independently verified, and a 2025 systematic review of smartwatch ECG accuracy covering Apple, Withings, Samsung, Fitbit, AliveCor, Amazfit, and Huawei did not include Garmin.
Which Tracks Sleep Stages More Accurately?
Where the evidence actually differs
The published comparison favors Fitbit on sleep stages, for one model of each brand. It comes from a review of separate studies rather than one study testing both watches on the same sleepers.
What published research found
Fitbit Charge 4 ahead in one reviewA systematic review of eight sleep-lab studies compared the Fitbit Charge 4, Garmin Vivosmart 4 and WHOOP against polysomnography. The Fitbit Charge 4 showed higher sensitivity to deep sleep (75 percent) and REM sleep (86.5 percent) than the other two, and the smallest REM disagreement, 4.0 minutes. The Charge 4 and the Vivosmart 4 both showed moderate accuracy for sleep stages and total sleep time.
In a 2025 meta-analysis of 24 sleep-lab studies covering both brands among others, the wearables as a group underestimated total sleep by about 17 minutes, and in a subgroup analysis Fitbit’s wake after sleep onset did not differ from polysomnography.
Neither source tested a current Garmin flagship such as a Fenix or Venu.
Schyvens et al., JMIR mHealth and uHealth, 2024 (doi:10.2196/52192) · Lee et al., Journal of Clinical Sleep Medicine, 2025 (doi:10.5664/jcsm.11460)What Fitbit Has That Garmin Doesn't
ECG across a wider current lineup
Fitbit's ECG spans Sense 2, Sense, Charge 5, and Charge 6; Garmin's is real but limited to select higher-end models.
Multi-input Stress Management Score
Calculated once daily from over 10 inputs across three categories, heart rate/EDA responsiveness, exertion balance, and sleep patterns, a broader input set than Garmin's continuous Stress Score.
What Garmin Has That Fitbit Doesn't
Race Predictor
Projects finish times from 5K to marathon using VO2 Max, training load, and performance history. No equivalent feature was found on Fitbit's page.
Flexible Pulse Ox timing
Garmin can run SpO2 on-demand or continuously depending on device settings. Fitbit's SpO2 percentage is sleep-derived only, with no daytime spot check.
Common questions
Is Fitbit or Garmin more accurate for heart rate?
Garmin measured closer. Across 158 publications covering nine brands, Apple Watch and Garmin were the most accurate for heart rate while Fitbit tended toward underestimation (JMIR mHealth and uHealth, 2021). This is the one metric of the four where Garmin leads, and the direction of Fitbit’s error is consistent rather than random, which matters more than the size of it: a reading that is reliably a little low still tracks change over time correctly.
Is Fitbit or Garmin more accurate for steps?
They miss in opposite directions, which is more useful than knowing which is closer. Worn together for 24 hours by adults over 65, the two agreed with each other almost perfectly (intraclass correlations above 0.89), yet the Fitbit Charge 2 overcounted by 12.36 percent while the Garmin vivosmart HR+ undercounted by 9.36 percent against the criterion (JMIR mHealth and uHealth, 2019). Across 65 reviewed studies the Fitbit Charge and Charge HR held mean absolute percentage error under 25 percent over 20 studies (Journal of Medical Internet Research, 2022). Step error also grows with real life for both brands: 8.2 percent on a treadmill, 9.9 percent over ground, and 18.48 percent across a free-living day (European Journal of Sport Science, 2017).
Is Fitbit or Garmin more accurate for calories burned?
Fitbit was clearly better of the two, and neither is good. In the head-to-head, Garmin returned poor agreement with the criterion for energy expenditure while Fitbit reached moderate-to-good agreement with a mean absolute percentage error of 12.25 percent, underestimating calories (JMIR mHealth and uHealth, 2019). Set that against the wider picture: energy-expenditure error exceeded 30 percent for every brand across 65 reviewed studies, and no brand was accurate across 158 publications (Journal of Medical Internet Research, 2022; JMIR mHealth and uHealth, 2021). Better here means less wrong.
Is Garmin or Fitbit more accurate for sleep?
Fitbit, on every sleep measure that has been compared directly. Agreement with the criterion was poor for both devices on sleep parameters except for Fitbit, which reached moderate agreement, with total sleep time error of 10.13 percent (JMIR mHealth and uHealth, 2019). Against polysomnography, the Fitbit Charge 4 had the smallest disagreement for REM sleep at 4.0 minutes and higher sensitivity to deep sleep at 75 percent and REM at 86.5 percent than the Garmin Vivosmart 4 (JMIR mHealth and uHealth, 2024). One number is worth stating plainly: on wake after sleep onset, the two brands erred in opposite directions and Fitbit was the more accurate of them at a mean absolute percentage error of 49.7 percent. Being the better of two devices is not the same as being right.
How does Fitbit vs Garmin GPS accuracy compare?
The evidence behind this page does not separate them on it. The head-to-head and the systematic reviews measured steps, heart rate, energy expenditure, moderate-to-vigorous activity minutes and sleep. Distance appears as an assessed outcome category in one review of 65 studies, but with no brand-level figures attached, and satellite positioning accuracy was not what any of these validations set out to test (Journal of Medical Internet Research, 2022). A step-count or heart-rate result does not transfer to GPS, so no comparison is drawn here.
Is Garmin better than Fitbit?
It depends which number you rely on, and the split is consistent across the evidence. Garmin measured heart rate more accurately. Fitbit was better on energy expenditure and on every sleep measure compared directly. On steps they agreed with each other closely while erring in opposite directions, Fitbit high and Garmin low. The more useful framing is that the gaps between these two brands are smaller than the gaps between a laboratory and ordinary life: step error roughly doubled from treadmill to free living for the devices tested, and energy-expenditure error exceeded 30 percent for every brand reviewed.
This page won't tell you which to buy. Price, app ecosystem, and design all matter to that decision and none of them are evidence questions, so none of them are covered here. What the evidence actually supports: Fitbit and Garmin measure resting heart rate over different windows, both now report an actual blood-oxygen percentage but on different measurement schedules, and each has one real feature (ECG for Fitbit, Race Predictor for Garmin) the other doesn't offer. For the full picture on either device, see the complete Fitbit or Garmin profile.
KnowYourPrime Evidence Registry: Finding KYP-ER-0001: Smartwatch Blood Oxygen (SpO2) Accuracy Against Arterial Blood (SaO2) · Finding KYP-ER-0003: Wearable HRV Accuracy Against ECG · Finding KYP-ER-0005: Readiness and Recovery Score Validity · Finding KYP-ER-0007: Wearable Sleep Tracking Accuracy Against a Sleep Lab · Finding KYP-ER-0009: Wearable Heart Rate Accuracy · Finding KYP-ER-0011: Wearable VO2 Max Estimate Accuracy · Finding KYP-ER-0016: Wearable Sleep Stage Accuracy · Finding KYP-ER-0024: Oura Ring HRV Accuracy Against ECG