Why your pace jumps around so much during a hike

The short answer

Average pace is total distance divided by total moving time, worked out once the walk — or a decent stretch of it — is behind you. It is a slow, stable number because it is built from a large amount of distance and a large amount of time, and small errors in either wash out. The live figure on a screen while you are still walking is a different calculation: distance and time over a short recent window, recomputed every few seconds. That responsiveness is exactly what makes it jump around, because a short window has very little distance and very little time to average anything over.

Neither number is wrong. The average is the honest one for judging the walk as a whole; the live one is closer to a rough gauge than a measurement, and it was never built to sit still.

Average pace and live pace are answering different questions

Ask "how fast did I walk today" and you want average pace — the whole route, start to finish, one number. Ask "how fast am I walking right now, this second" and you want live pace, which has to answer using only whatever has happened in the last few points, because that is all it has to work with. The second question is harder to answer well, because a handful of recent points is a small, noisy sample compared with an entire route.

The same tension shows up with distance and elevation gain, and for the same underlying reason: a total computed from a whole recording is far steadier than any figure that only looks at the last few seconds.

Why a few metres of GPS noise turns into a big pace swing

A GPS fix on a phone typically lands within a few metres of your true position, not exactly on it. Over a kilometre of walking, that handful of metres of wobble is a rounding error — well under one percent of the total distance, and it barely moves the average. Over the few metres you actually cover in two or three seconds, the same wobble is a much bigger share of a much smaller number. Speed is distance over time, so when the distance in the calculation is small, ordinary GPS noise can look like you sped up or stopped dead, when in fact your stride never changed at all.

This is the same reason a recorded track zigzags a little on a straight path even when nothing is wrong with the phone or the app: the noise is always there, and it only becomes visible when the window you are measuring across is short enough that it cannot be averaged away.

Why hills genuinely slow your pace, separately from any noise

Some of the swing in pace on a hilly trail is real, not noise. On a climb, part of every stride goes into gaining height rather than covering ground, so the horizontal distance you rack up for a given amount of walking is smaller than it would be on the flat — and pace, being distance over time, slows down as a direct result. Coming back down, the opposite happens. None of this means your walking changed; it means the ground under your feet did, and pace on a hilly route was always going to look uneven compared with the same route on the flat.

This is worth knowing on its own, separately from the GPS-noise problem above: a pace figure that dips on every climb and picks up on every descent is describing the terrain accurately, not misbehaving.

Which number to actually trust

For judging a walk after the fact, or comparing one outing with another, use average pace over the whole route, or at least over a long enough stretch that a few seconds of noise cannot dominate it. Treat the live number on screen as a rough sense of the moment rather than something to chase or correct against — it was built to be responsive, not to be steady, and those two things trade off against each other by nature.

TrailCam reports pace per kilometre or mile as part of a route's summary, alongside distance, moving time and the elevation profile, and can also speak distance and pace aloud as you go if you want the number without looking at the screen.