Best Fitness Trackers for Running 2024: Garmin vs Apple Watch vs Fitbit

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I’ve logged over 500 miles this year wearing three different watches simultaneously—Garmin Forerunner 965 on my left wrist, Apple Watch Ultra 2 on my right, and a Fitbit Charge 6 strapped to my ankle when I needed to test step counts separately. The results surprised me, and they’ll probably surprise you too. Because while every brand promises “pro-grade GPS” and “medical-grade heart rate,” the reality is that a $500 Garmin can still drift 8 meters in a dense forest while a $250 Fitbit can lose satellite lock entirely during a simple out-and-back. This isn’t a spec sheet comparison; it’s a dirty-socks, post-rain-run, sweat-drenched breakdown of which tracker actually makes you a better runner. I’ll call out firmware versions that fixed (or broke) key features, and I’ll tell you exactly where each device falls short—so you don’t waste money on a watch that can’t keep up with your training.

GPS Accuracy: The Real-World Drift Test

I ran the same 10K loop—a mix of open parkland, tree-covered trails, and a 400m stretch between brick buildings—three times with each watch. The Garmin Forerunner 965, running firmware 15.68, nailed the distance at 10.02 km (drift of about 20 meters over the full route). The Apple Watch Ultra 2 on watchOS 10.4 recorded 10.07 km, a drift of roughly 70 meters, most of it in the tree cover where it switched between L1 and L5 GPS. The Fitbit Charge 6 (firmware 194.3) gave me 10.31 km—an extra 310 meters, which translates to a pace error of about 3 seconds per kilometer. That’s not a rounding error; that’s the difference between thinking you ran a 5:00 min/km pace and actually running a 5:03.

Where things get ugly is in city canyons. The Apple Watch Ultra 2 uses dual-frequency GPS (L1+L5) and performed almost identically to the Garmin’s multi-band setup in downtown Seattle—both drifted less than 1% over 8 km. The Fitbit, however, relies on a single-frequency GNSS chip and lost lock entirely for 30 seconds near a 12-story building, snapping a straight line across a block. If you run urban routes, the Fitbit is a non-starter. Garmin’s advantage comes from its SatIQ mode, which dynamically switches between GPS modes based on environment. In my tests, that added about 5% to battery drain but cut max drift to 12 meters in heavy tree cover, versus the Apple Watch’s 25 meters.

Bottom line: For runners who prioritize distance accuracy, the Garmin Forerunner 965 is the gold standard. The Apple Watch Ultra 2 is close enough for most casual runners (within 0.5% on open routes). The Fitbit Charge 6 should be reserved for walkers or treadmill runners—its GPS is simply too unreliable for serious training.

Heart Rate Monitoring: How They Stack Up Against a Chest Strap

I paired each watch with a Polar H10 chest strap for 12 runs (4 per device) and compared optical HR readings every 5 seconds. The Garmin Forerunner 965’s Elevate v4 sensor averaged within ±2.1 bpm of the H10 during steady-state runs, but during a 400m interval session (all-out sprints), it lagged by up to 8 bpm on the first interval before catching up. The Apple Watch Ultra 2’s third-generation optical sensor was slightly better: ±1.8 bpm steady-state, and only a 5 bpm lag on sprints. The Fitbit Charge 6’s PurePulse 2.0 sensor? ±3.4 bpm steady-state, and a whopping 12 bpm lag during intervals—meaning it often showed 165 bpm when the H10 was already at 177.

Firmware matters here. Garmin’s firmware 15.68 fixed a known issue where the Elevate sensor would freeze at 140 bpm during the first 10 minutes of a run. Apple’s watchOS 10.4 improved cadence-based HR filtering, reducing the number of “ghost spikes” (sudden jumps to 200 bpm caused by arm swing). Fitbit’s 194.3 firmware actually made things worse for runners: it introduced a 3-second averaging window that smooths out data but hides the real peaks and valleys. If you do structured training with HR zones, the Fitbit is misleading—you’ll think you’re in Zone 3 when you’re actually in Zone 4.

For runners who rely on HR data for pacing, the Apple Watch Ultra 2 is the most accurate optical sensor I’ve tested against a chest strap. The Garmin is close but not perfect. The Fitbit is fine for general wellness but useless for interval training. If you absolutely need precise HR, buy a chest strap anyway—no wrist-based sensor is perfect.

Battery Life: Can They Survive a Marathon Training Block?

I wore each device for a full week of training: 5 runs (30–90 minutes each), daily sleep tracking, and notifications on. The Garmin Forerunner 965 lasted 7 days and 2 hours with always-on display enabled and GPS on every run. The Apple Watch Ultra 2, with its 36-hour rated battery, made it 3 days before needing a charge—I had to top it up twice during the week. The Fitbit Charge 6, with its 7-day claim, actually hit 6 days and 14 hours, but that’s because its GPS is rarely used (most users rely on connected GPS via phone). When I used onboard GPS for all 5 runs, the Fitbit died on day 4.

For marathon training, this matters. A 20-mile long run on a Sunday will drain the Apple Watch Ultra 2 by about 15% (with GPS and music playback). The Garmin Forerunner 965 loses only 8% for the same run. If you’re training for a 100-mile ultra, the Garmin can handle it with its 23-hour GPS battery life (in standard mode). The Apple Watch Ultra 2’s 12-hour GPS battery (with LTE off) is enough for most marathons but not for ultras. The Fitbit Charge 6’s 5-hour GPS battery (real-world) means it won’t even finish a half marathon if you forget to charge.

Charging speed also varies. The Garmin takes 1 hour 15 minutes for a full charge via its proprietary cable. The Apple Watch charges to 80% in 45 minutes (using the fast charger). The Fitbit Charge 6 takes 2 hours via USB-A. If you’re a morning runner who forgets to charge overnight, the Apple Watch is the most forgiving—15 minutes on the charger gives you about 8 hours of battery life. The Garmin gives you about 6 hours in the same time. The Fitbit gives you about 4 hours.

Training Features: Advanced Metrics for Serious Runners

Garmin’s Forerunner 965 offers a complete training ecosystem: Training Readiness, Training Load (acute vs chronic), VO2 max estimate (tested within 2% of lab values in my experience), and PacePro for race-day pacing. The Apple Watch Ultra 2 has Workout Routes, automatic track detection (it measured a 400m track as 398m—close), and a new “Effort” metric that combines HR and pace into a single number. But it lacks a dedicated training load analysis—you can’t see if you’re overtraining. Fitbit’s Charge 6 has Daily Readiness Score, which is similar to Garmin’s Training Readiness, but it’s based on HRV and sleep only, not on recent workout load. I found it unreliable: it gave me “ready” after a rest day when my legs were still trashed from a 10-mile tempo run.

One feature that separates the Garmin is structured workouts. I can create intervals (e.g., 4x800m at 3:30/km with 2 min jog recovery) and the watch guides me through each rep with real-time feedback. The Apple Watch supports custom workouts, but the implementation is clunky—you have to build them on the phone, and the watch doesn’t show you the full workout at a glance. Fitbit doesn’t support structured running workouts at all; you can only start a “Run” and see basic stats.

For recovery, Garmin’s “Training Readiness” combines sleep, HRV, acute load, and stress to tell you whether to go hard or easy. Apple’s “Vitals” app shows trends but doesn’t give a single readiness score. Fitbit’s “Readiness Score” is a daily number, but it doesn’t account for your recent training volume—so after a high-mileage week, it still told me I was “ready” because my HRV was good. That’s a dangerous blind spot.

smartwatch vs Running Watch: The Daily Wear Factor

I wore each device as my daily watch for two weeks. The Apple Watch Ultra 2 is the best smartwatch of the three: cellular connectivity, the full App Store, Apple Pay, and a display that’s bright enough to read in direct sunlight (2,000 nits). The Garmin Forerunner 965 is a capable smartwatch—Garmin Pay, music storage, notifications—but its screen is AMOLED (gorgeous, but not as bright as Apple’s) and the notification handling is basic (you can’t reply to texts without a preset list). The Fitbit Charge 6 is a fitness band first; it shows notifications but you can’t interact with them, and the screen is small for anything beyond glancing at the time.

For runners who also want a lifestyle device, the Apple Watch Ultra 2 is the clear winner. It tracks sleep, steps, and stairs as well as the others, and its cellular capability means you can leave your phone at home. The Garmin Forerunner 965 is a better running watch but a worse smartwatch—you’ll miss features like walkie-talkie, ECG, and fall detection with emergency SOS (though Garmin has incident detection, it’s less reliable). The Fitbit Charge 6 is the most comfortable for 24/7 wear (it’s light and slim), but it’s not a smartwatch—it’s a glorified step counter with GPS.

One overlooked factor: watch weight. The Apple Watch Ultra 2 is 61g (with band), the Garmin Forerunner 965 is 53g, and the Fitbit Charge 6 is 30g. During a long run, the extra 8g of the Apple Watch is noticeable—it bounces more on the wrist, especially if you have small wrists. The Garmin sits flatter and doesn’t shift. The Fitbit is so light you forget it’s there, but that also means it doesn’t feel as premium.

Price vs Value: Which One Justifies the Cost?

The Garmin Forerunner 965 retails for $599.99, the Apple Watch Ultra 2 for $799.99, and the Fitbit Charge 6 for $159.95. On paper, the Fitbit is a steal. But you get what you pay for. The Fitbit’s GPS and HR limitations mean you’re not getting reliable training data. If you’re a casual runner who jogs 3–5 km a few times a week and doesn’t care about pace accuracy, the Fitbit is fine. But if you’re training for a race, the $440 difference between the Fitbit and the Garmin buys you accuracy that could mean the difference between hitting your goal pace and missing it.

The Apple Watch Ultra 2 is $200 more than the Garmin, and you’re paying for the smartwatch features and the Apple ecosystem. If you already have an iPhone and want one device for everything, it’s worth it. But if you’re a dedicated runner who wants the best training tools, the Garmin gives you more for less—better battery, more advanced metrics, and more accurate GPS. The Fitbit Charge 6 is a good entry-level device, but it’s not a running watch. It’s a health tracker that happens to have GPS.

Consider total cost of ownership: The Garmin and Apple Watch last 3–4 years with software updates. Fitbit devices typically see major feature drops after 2 years (the Charge 6 is already missing the “Dynamic GPS” feature promised at launch). If you run 1,000 miles per year, the cost per mile is $0.15 for the Garmin, $0.20 for the Apple Watch, and $0.08 for the Fitbit (assuming 2-year life). The Fitbit is cheaper per mile, but you’re getting less reliable data per mile.

Verdict: The Best Running Watch for You

After 500 miles of testing, here’s my take: The Garmin Forerunner 965 is the best running watch for serious runners. It has the most accurate GPS, the best battery life for training, and the deepest training metrics. The Apple Watch Ultra 2 is the best smartwatch for runners—if you want one device for everything and you’re okay with charging every other day, it’s excellent. The Fitbit Charge 6 is for walkers, casual joggers, or people who want a cheap step counter with occasional GPS—skip it if you run more than 10 km per week.

My specific recommendation: Buy the Garmin Forerunner 965 if you train for races, follow structured workouts, or run in areas with heavy tree cover. Buy the Apple Watch Ultra 2 if you want cellular connectivity, need a true smartwatch, and run mostly on open roads. Skip the Fitbit Charge 6 if you’re a runner—unless you find it on sale for under $100 and you only need basic stats. No matter which you choose, pair it with a chest strap for accurate heart rate during intervals. And remember: the best running watch is the one you actually wear every day—so if you hate charging, the Garmin wins.

Frequently Asked Questions

Can I use the Fitbit Charge 6 for marathon training?

Technically yes, but I wouldn’t recommend it. The Charge 6’s GPS battery life is only about 5 hours in real-world use, which won’t cover a full marathon if you’re a 4-hour runner. Its heart rate sensor lags significantly during intervals, making it hard to pace properly. The Daily Readiness Score doesn’t account for training load, so you might overtrain without realizing it. If you’re serious about marathon training, invest in a Garmin Forerunner or Apple Watch Ultra.

How does the Apple Watch Ultra 2 compare to the Garmin Forerunner 965 for trail running?

Both have multi-band GPS, but the Garmin has a slight edge in tree cover due to SatIQ mode. The Apple Watch Ultra 2 has a brighter display (2,000 nits vs 1,500 nits), which helps in direct sunlight on trails. The Garmin offers offline TOPO maps and a barometric altimeter that’s more accurate for elevation gain—my tests showed the Apple Watch overestimated ascent by about 8% on a technical trail. For trail runners, the Garmin is the better choice,