What’s your real race time?

Updated July 9, 2026 · By the Runked team

Every runner wants the same number: if I raced today, what would I run? It decides your goal pace, your pacing plan and whether that PR is realistic. The trouble is that most tools answer it badly.

Why static calculators mislead

Type your 5K time into a classic race calculator and it will confidently hand you a marathon time. Under the hood it is usually the Riegel formula, 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 three weeks later, after a big block or a week off, is different, and the calculator has no idea.

A one-race extrapolation is a fine sanity check. It is a poor training partner.

Fitness-based prediction, explained

The better 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. That is the same class of sports-science modelling coaches use, and it has three advantages:

• It updates continuously, so the number reflects the runner you are this week.
• It rewards consistency and quality, not a single peak day.
• It is honest when you detrain, so you do not toe the line chasing a pace you no longer own.

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. The clock you bank early by going out too fast is always repaid with interest.
• 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. Chasing a marathon time? The long run and marathon-pace efforts move that projection far 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 live in Runked PRO, which comes with a 7-day free trial. Your running rank, GPS tracking, leagues and streaks are free forever.

Frequently asked questions