What’s your real race time?
A race time predictor estimates your finish time from your current fitness. Runked projects your 5K, 10K, half marathon and marathon times from your actual training history and updates them after every run. As your fitness builds, each projection shows a delta so you can see exactly how much time you are gaining.
A projected finish time sets your goal pace, your pacing plan, and whether a PR is realistic: if I raced today, what would I run? The problem is how that number gets produced.
Whether the number it hands back is any good is a separate question, and one a predictor cannot answer: that needs the published finisher data, which is laid out for the 5K and the marathon by age, sex and percentile.
A finish time can also be read against your age: age grading turns it into a percentage of the fastest time recorded for that age, sex and distance.
Why static calculators mislead
Type your 5K time into a classic race calculator and it will hand you a marathon time. Under the hood it applies the Riegel formula (Riegel, American Scientist, 1981), T2 = T1 × (D2 / D1)^1.06, extrapolated from one race. Those tools have two blind spots:
- They assume distance-specific fitness you may not have. Predicting a marathon from a 5K assumes you can hold a hard effort eight times longer. Without long runs and marathon-pace work, you cannot, and the formula flatters you by minutes.
- They freeze one moment in time. A single race captures one day. Your fitness weeks later, after a big training block or a week off, is different, and the calculator has no idea.
A one-race extrapolation works only as a quick sanity check.
Fitness-based prediction, explained
A fitness-based approach models your training load over weeks and asks what finish times that level of fitness supports. Instead of trusting one race, it reads the whole training block: how much you run, how hard, and how consistently.
| One-race calculator | Fitness-based prediction | |
|---|---|---|
| What it reads | A single race time, extrapolated with the Riegel formula. | Weeks of training load: how much you run, how hard, and how consistently. |
| When it changes | Only when you race again. | After every synced or tracked run. |
| What it assumes | That you have the distance-specific fitness to hold the effort eight times longer. | Nothing beyond the training you have actually done. |
| After a break in training | The old race time still stands; the calculator has no idea. | Projected times drift slower until fitness rebuilds. |
How to use a prediction on race day
A prediction is a target, and how you spend it decides whether you hit it:
- Start conservative. Run the first portion a touch slower than predicted pace, especially in a half or marathon. Going out too fast costs more time late than it saves early.
- Even or negative split. Aim to run the second half as fast or faster than the first. Predictions assume smart pacing; a reckless first 5K breaks the model.
- Adjust for conditions. Heat, wind and hills all cost time. Treat the projection as an ideal-conditions number and give yourself margin on a hard day.
How predictions improve
Because the projection tracks fitness, making it faster is a training problem with known levers:
- Consistency. Weeks without gaps build the chronic fitness the model reads. Missed weeks cost more than any single workout adds.
- Quality sessions. Tempo runs, threshold work and intervals push the ceiling that easy miles alone will not. See the types of running workouts and where each fits.
- Distance-specific work. For a marathon goal, the long run and marathon-pace efforts move that projection more than a fast 5K does.
How Runked does it
Connect Garmin Connect or Apple Health and Runked reads your training history, then projects your 5K, 10K, half and marathon times in the Performance section. Each one carries an improvement delta, so a half marathon projection of 1:12:58 that shows −10:12 tells you at a glance that ten minutes of fitness have arrived since you started. Every synced or tracked run refreshes the numbers, and pairing them with a training plan turns the projection into a plan of attack.
Race time predictions are part of the Runked subscription, which starts with a 7-day free trial on the yearly plan. Compare to yourself, not to others: in Runked, the running rank depends only on your own running, and so does the projection.
See your projected times
Download Runked, connect your watch, and start the yearly plan's 7-day free trial to project your 5K to marathon finish times.
Download on App StoreFrequently asked questions
How accurate are race time predictors?
A race time predictor lands closest to your real finish when your training has been consistent and specific to the distance. Over the marathon, fueling, pacing and the wall introduce variables no model can see. Treat a prediction as a well-informed estimate; race day still decides the final result.
Can I predict my marathon time from a 5K?
You can extrapolate a rough marathon time from a 5K, but it assumes you have the endurance to hold pace 8 times longer, which is unlikely without marathon-specific long runs. A single-race formula flatters your marathon time. A prediction built from weeks of training load reads your endurance from the training you have done.
Why did my predicted time get slower?
Predictions track your current fitness, so they move both ways. After a break, an illness or a heavy fatigue block, your projected times can drift slower. That is the model being honest. String together consistent quality training and the deltas turn green again as fitness rebuilds.
Is the race predictor free?
No. Race time predictions are part of Runked PRO, and one subscription covers everything in the app: $59.99 a year after a 7-day free trial, or $11.99 a week. That includes your running rank, GPS tracking, streaks, personalized plans and performance analytics.