Strava vs Garmin vs PIRX: Which Race Prediction Should You Trust?

Here is the one-line difference: Strava tells you what you did. Garmin shows your data. PIRX tells you why it happened and what's next — with validated prediction accuracy of 98% across PIRX users.

All three can estimate your race time. But they answer different questions. The table below shows what each tool is good at and what it misses.

Tool	Tells you	Misses
Strava	What you did — your runs, history, and best efforts	Why your races unfold the way they do, and what to fix next
Garmin	Your data — VO2max estimate, training status, device numbers	Often runs optimistic; can't see your race-day pacing, fueling, or heat
PIRX	Your projected finish and a supported range — plus why and what's next	Needs one recent race time to start (but it's free, no device)

The one-line difference

Think of it this way. Strava is your logbook. It records every run and lets you compare efforts and segments. Garmin is your dashboard. It reads your watch and shows numbers like VO2max and training status. PIRX is your projection. It takes a recent race and tells you what you can run next, with a range you can trust.

Each one is useful. But only one is built to answer "what should my goal be, and why?"

What Strava and Garmin show vs what PIRX projects

Strava added a Performance Predictions feature. It reads your full run history and your best efforts to estimate finishes for the 5K, 10K, half, and marathon (Runner's World). Strava says short-race predictions came within about 3% in testing. That is solid for a 5K. It leans on having lots of logged runs.

Garmin builds its Race Predictor from your watch's VO2max estimate, your training history, and your records (Garmin Support). The catch is the VO2max estimate carries about a 5% error (the5krunner), and many runners find the times optimistic — your watch cannot feel a hot day or a hard final 10K.

PIRX does not need a watch at all. You enter one recent race time, and PIRX projects your finish at any distance with a supported range — free, no signup. It learns your style instead of using one fixed formula.

Why "why + what's next" matters

A number alone does not make you faster. You also need to know why and what to do.

Say your goal feels just out of reach. Strava shows your past runs. Garmin shows a target time. PIRX shows a realistic range and, in the full app, breaks down the drivers behind it — your training volume, recovery, and durability — so you know what to work on.

That is the real gap. Strava and Garmin describe. PIRX projects and explains. When you know the why, you can fix the right thing instead of guessing.

Try the projection

You do not need to pick just one tool. Keep logging in Strava. Keep your Garmin numbers. But when you want an honest, explainable projection, use PIRX — free, no signup, no wearable needed.

Enter a recent 5K, 10K, half, or marathon and see your projected times across every distance. It takes seconds.

New here? Start with the complete guide to predicting your race time. Wondering if your goal fits? Read is my goal time realistic. Want to nail the race itself? See how to pace a marathon.

Sources

• Garmin Support. How are race prediction times determined on my watch? (VO2max estimate + training history + personal records.)
• the5krunner. Garmin Race Predictor (Notes ~5% mean error in the underlying VO2max estimate.)
• Runner's World. Strava's Performance Predictions and setting race-day goals (How Strava predicts from all-run history and top efforts.)
• Lifehacker. I compared Garmin and Strava's race-day predictions (Both estimate 5K–marathon by translating your run history.)