Best watches for your first marathon

A first marathon asks three things of a watch. It has to carry a plan for months, show a pace you can believe, and last one morning. The last is easy.

I haven't worn any of these. What follows comes from maker pages and published studies, checked on 3 November 2026. This page covers one race goal, so if you want a watch for general life, this isn't the list. If you're still unsure which kind of device you need, the picker asks about your training first, and the marathon goal page has the wider set.

Battery won't decide this

At 5:30 min/km, 42.2 km (26.2 mi) takes about 3 h 52 min. At 7:30 min/km it takes about 5 h 17 min.

The shortest figure on this page is the Forerunner 170, and even that maker's claim covers the slower finish nearly four times over. Spend your attention elsewhere. Longer-race sums are in how to choose a GPS mode.

These modes differ, so read the hours as a rough guide. Garmin's figure is GPS only, Polar's is its Performance training mode, and Coros and Suunto quote all satellite systems.

The plan is the real choice

Pick the plan first. Then pick the watch that runs it.

Garmin's release for the Forerunner 70 and 170 says Coach plans adapt daily from health and recovery metrics. It also says Run Coach now has run/walk workouts and lower-volume plans. If you're coming up from 5 km (3.1 mi), I'd start there, because a plan that bends after a bad week is easier to keep going for four months.

Two things I couldn't confirm from that release: the exact plan lengths, and whether any of this sits behind a paid Connect+ tier on these two watches. Check both in Garmin Connect before you buy.

Coros's UK page lists personalised marathon plans, structured workouts and building your own plan, which also suits you if you already follow a book or a coach. Polar lists a Running Programme on the Pacer, and calls it personalised and adaptive. Suunto's page for the Run 2 talks about executing a race plan and doesn't name a built-in one.

Two comparisons go further on this: Forerunner 70 vs 170 and Forerunner 170 vs Coros Pace 4.

How far to trust the pace

I found no peer-reviewed test of these five for race pace. Tom's Guide (independent, non-peer-reviewed) says the Suunto Run 2's distance and pace sat in line with a Fenix 9 Pro and a Coros Pace 4, but that's one tester with no figures.

The nearest peer-reviewed distance test is Gilgen-Ammann 2020, part-funded by Polar, which the paper says had no influence on the outcome. It put eight watches from the 2019 era through measured routes and found average errors of 3.2% to 6.1%, worst in cities and forest. None of the five here was in it, and those results don't transfer to them.

Pobiruchin 2017, also peer-reviewed, surveyed runners after one half marathon in 2016. Watches were about 0.12 km off on average, against 0.35 km for phone apps. Those were runner-reported figures from an open course, and nobody runs the exact measured line, so that gap isn't pure GPS error.

Pace is weaker still. Average pace over a longer effort inherits distance error. Instant pace is noisier, and I haven't found solid independent numbers for it.

The same goes for multi-band GPS, which the Pace 4 and Run 2 have. I found no independent peer-reviewed figure for how much it helps on current watches. Don't pay for it expecting a measured gain.

Don't race your predictor

The Garmins and the Coros list a race predictor. Treat its finish time as a guess.

In Howard 2026, peer-reviewed and read as an abstract only, 20 people wore a Forerunner 265. Its half-marathon predictions came out significantly fast: 129.97 min predicted against 137.55 min actual, though the authors put the error under 10%. A different watch, so it says nothing direct about these. Still, set your opening pace from your long runs and from the plan, which is what I'd do with any predictor.

Heart rate on a steady run

Marathon pace is the kind of steady effort wrist sensors handle best. Zhang 2020, a peer-reviewed meta-analysis of 44 articles and 15 brands, found a mean difference of -0.51 bpm on the treadmill (95% CI -1.60 to 0.58). Averages hide individual error, though, and the models tested are largely discontinued. I found no peer-reviewed test of these five in that setting, only reviewers' runs, which aren't peer-reviewed.

A tracker isn't a medical device. Wearable readings are estimates for general fitness and wellness. If you have a heart condition, follow your care team's guidance on training zones and not a watch reading.

What I'd buy

New to running and likely to need a plan that adapts: the Forerunner 70. Swimming too: the Forerunner 170. Already following a written plan and wanting hours to spare: the Pace 4, as long as your strap speaks Bluetooth.