Guide · Smartwatches
Do you need a running watch if you have a phone?
For a lot of runners, no. Here is the specific point at which the answer changes.
A modern phone has the same satellite receivers as a mid-range running watch and a far better processor. If your running consists of going out for forty minutes and wanting to know afterwards how far you went, a phone in an armband does that job accurately and you can stop reading here.
Three things change the answer, and none of them is accuracy.
Real-time pace is the whole product
The first is real-time feedback. A watch tells you your current pace at a glance mid-stride; a phone does not, in any usable way. If you are doing structured sessions — intervals, tempo efforts, anything with a target pace — that glance is the entire product. Without it you are running by feel and checking afterwards, which is fine for easy running and useless for a session.
Continuous heart rate, and the friction argument
The second is heart rate, and specifically continuous heart rate. Optical wrist sensors are imperfect and are still far better than nothing; a phone in your pocket measures nothing at all. If you train by heart-rate zones, or if you want recovery and training-load metrics that mean anything, this is the point at which a watch stops being a convenience and starts being the instrument.
The third is battery and weight, and it is the mundane one that decides most purchases in practice. A phone strapped to your arm for ninety minutes is heavy, hot, and using its battery for GPS at exactly the rate you would expect. A watch weighing forty grams runs for a fortnight. That is not a performance argument, it is a friction argument, and friction is what decides whether you go out.
What a watch does not buy you is accuracy on an ordinary route. If you run in open terrain, a good phone and a mid-range watch will produce tracks you cannot tell apart. The accuracy argument only becomes real in cities, where dual-band reception matters — and that is a specification worth checking rather than a category worth assuming.
The honest summary: if you run to feel better, use your phone. If you run to get faster, buy the watch, and buy it for the pace screen rather than for the satellite chip.