🎯 Finish Time Predictor
See your race potential at any distance based on a recent result
Select your goal race to highlight that prediction, or leave blank to see all equally.
| Distance | Riegel | Cameron | VDOT | Pace |
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How to Use This Calculator
Using the finish time predictor is pretty straightforward:
- Enter a recent race result – Pick a race you’ve run in the last 3-6 months where you gave it a solid effort. A 5K, 10K, half marathon, or even a timed mile works great.
- Select your goal race (optional) – Training for something specific? Select it from the dropdown and we’ll highlight that prediction for you.
- Hit calculate – You’ll see predicted times for everything from the mile to the full marathon, plus your VDOT score (more on that below).
- Compare methods – Toggle between Riegel, Cameron, and VDOT formulas to see how different prediction models stack up.
What is a Race Time Predictor?
Here’s the deal: your performance at one distance tells us a lot about what you’re capable of at other distances. A race time predictor uses mathematical formulas to convert your known result into equivalent performances across different race distances.
Think of it like this – if you just crushed a 25-minute 5K, that performance represents a certain level of fitness. That same fitness level translates to roughly a 52-minute 10K, a 1:55 half marathon, or about a 4:00 marathon (assuming you train properly for those distances).
The math behind it isn’t magic – it’s based on decades of research into how running pace naturally slows as distance increases. Your body can only maintain that 5K effort for so long before it needs to dial back.
The Three Prediction Methods Explained
Our calculator gives you three different predictions because, honestly, no single formula is perfect. Here’s what each one does:
Riegel Formula
This is the classic. Pete Riegel published this formula in Runner’s World back in 1977 and it’s still the most widely used prediction method today. The formula is beautifully simple: T₂ = T₁ × (D₂/D₁)^1.06
Translation? Your pace slows by about 6% every time the distance doubles. It’s remarkably accurate for distances from 5K to half marathon and tends to work well for most recreational runners.
Cameron Formula
Dave Cameron developed this formula by analyzing world-class performances across multiple distances. It tends to predict slightly slower times at longer distances compared to Riegel, which actually makes it more realistic for many runners tackling their first marathon.
If you’re predicting marathon times from shorter races, Cameron might give you a more honest (if humbling) estimate.
VDOT Method
This one comes from legendary coach Jack Daniels and his “Running Formula” book. VDOT isn’t quite the same as VO2max, but it’s related – it’s essentially a measure of your running fitness based on race performance.
What’s cool about VDOT is that it accounts for running economy, not just aerobic capacity. Two runners might have the same VO2max in a lab, but different VDOT scores based on how efficiently they actually run.
Understanding Your VDOT Score
When you use the calculator, you’ll see a VDOT number pop up. Here’s what it means:
- 30-35: Beginner to recreational runner
- 35-40: Solid recreational runner
- 40-45: Competitive age-group runner
- 45-50: Serious competitive runner
- 50-55: Highly competitive / local elite
- 55-60: Regional/national level
- 60+: Elite / professional level
Your VDOT score is useful beyond just predicting race times. Coach Daniels uses it to prescribe training paces – your easy runs, tempo efforts, and interval workouts can all be dialed in based on your current VDOT.
Which Prediction Should I Trust?
Good question. Here’s my honest advice:
For 5K to half marathon predictions: All three methods tend to be pretty close. Go with whichever feels most realistic based on what you know about your training.
For marathon predictions from shorter races: Be cautious. The formulas assume you’ve trained properly for the marathon distance, including those crucial long runs and race-specific workouts. If you’re predicting a marathon time from a 5K and you’ve never run more than 10 miles, the prediction is optimistic at best.
When predictions disagree significantly: Pay attention to the slower one. It’s better to start a race conservatively and finish strong than to blow up at mile 20 because a calculator told you that you could run faster than you actually can.
Why Predictions Get Less Accurate at Longer Distances
Here’s something important to understand: predicting a 10K from a 5K is way more accurate than predicting a marathon from a 5K. Why?
The training factor. Running a good marathon requires specific adaptations – glycogen storage, fat oxidation, mental toughness, fueling strategy – that you simply don’t need for a 5K. Two runners with identical 5K times could have vastly different marathon potentials based on their endurance training.
The execution factor. There’s more that can go wrong in a marathon. Nutrition, hydration, pacing, weather, chafing, bathroom breaks – the longer the race, the more variables come into play.
The experience factor. Running a smart marathon takes practice. First-time marathoners almost always run slower than the formulas predict, and that’s totally okay.
Tips for Getting the Most Accurate Predictions
Use a recent race. Performances from 3-6 months ago reflect your current fitness best. That PR from three years ago? Not so useful.
Use a race, not a training run. There’s something about a race atmosphere – the adrenaline, the competition, the taper – that brings out performances you can’t replicate in training. A time trial works in a pinch, but a real race is better.
Match the conditions. A fast, flat 5K on a cool morning doesn’t translate perfectly to a hilly half marathon in July heat. Keep course and conditions in mind.
Be honest about effort level. Did you go all-out, or were you holding back? The predictions assume a maximal effort.
Going Up vs. Going Down in Distance
This calculator works both directions, and that’s important:
Marathon runner trying a 5K? You might be surprised how fast you can go. Marathon training builds a massive aerobic engine, and when you only have to sustain effort for 20-30 minutes instead of 4+ hours, you’ve got gears you haven’t used in a while.
5K runner thinking about a marathon? The prediction gives you a target, but you’ll need to put in the distance work to actually achieve it. Those long runs aren’t optional.
Common Questions
Q: The calculator says I can run a 3:30 marathon but I’ve never run more than 10 miles. Is that realistic?
It’s your potential based on fitness, but potential and reality are different things. You’d need 4-6 months of proper marathon training to have a shot at that time. Start with a more conservative goal for your first marathon.
Q: My predictions seem way off from what I actually ran. What gives?
Could be a few things: the input race wasn’t a true max effort, conditions were very different between races, or you weren’t properly trained for the longer distance. Also, bad race days happen – one result doesn’t define you.
Q: Which distance gives the most accurate predictions?
Generally, the closer your input race is to your target race, the more accurate the prediction. A 10K predicts a half marathon better than a 5K does. A half marathon predicts a marathon better than a 10K does.
Q: Should I use these predictions for race-day pacing?
Use them as a starting point, but adjust based on conditions and how you feel. If you go out at predicted pace and it feels too hard in the first few miles, slow down. Trust your body over the math.
Q: Why is my VDOT different from my actual VO2max test?
VDOT incorporates running economy, which a lab VO2max test doesn’t capture. You can have a moderate VO2max but excellent economy and still have a high VDOT. It’s a more practical measure of running fitness specifically.
Ready to Put Your Prediction to the Test?
Now that you know what you’re capable of, it’s time to train for it. Check out our other tools:
- Race Pace Calculator – Get mile-by-mile splits for your goal time
- Training Zones Calculator – Find your optimal training paces based on VDOT
- Marathon Finder – Find your next race