Race day preparation involves a lot of arithmetic: converting goal times to per-mile paces, generating split targets at each mile marker, predicting marathon times from 5K results, and calculating the first-half pace for a negative split plan. Most runners do this with a phone calculator and some mental math. These tools do it better, for free.
1. EvvyTools Pace & Race Time Calculator
EvvyTools provides a pace and race time calculator that handles the core pacing calculations in one place: input your goal finish time and race distance, and it generates the per-mile pace, cumulative split times at key distance markers, and first-half and second-half split targets for a planned negative split.
The tool also runs race predictions using Riegel's formula -- enter a recent race result and it returns predicted finish times for 5K, 10K, half marathon, and full marathon distances, along with the corresponding target paces. This makes it useful both for planning a specific race and for deriving training pace zones from a recent time trial.
What makes it worth bookmarking: the output is in the format you actually need on race day -- cumulative split times you can write on your arm or program into a pace band -- rather than just a single predicted time.
2. Runner's World Race Time Predictor
Runner's World includes a race time predictor built into its training tools section. Input a recent race time and the target race distance, and it returns a predicted finish time using a variation of Riegel's formula.
The Runner's World tool is reliable for the core calculation, though it does not generate per-mile split targets or cumulative times as its primary output. For that, you need to pair it with a separate pace calculator. The strength of Runner's World as a resource is the surrounding training content: articles on how to interpret predictions and adjust them for training volume, race conditions, and experience level.
3. World Athletics World Records Reference
Understanding how elite athletes pace races helps contextualize your own targets. World Athletics maintains the official database of world records at all distances, including the split times from record-setting performances.
Looking at how a world record marathon was paced -- what the 5K, 10K, and half marathon split times were in the final record -- illustrates the negative split principle in its most refined form. Elite performers do not go out fast and hang on; they pace with precision and build in the second half. The World Athletics records database makes this data accessible.
Photo by herbert2512 on Pixabay
4. Strava's Training Analysis Tools
Strava is primarily a training log and social platform, but its analysis tools are genuinely useful for pacing work. The segment analysis feature lets you compare your pace across the same course section at different points in a run or race, which is a direct way to measure whether you are running even, positive, or negative splits consistently.
The fitness and freshness graphs track your training load over time, which is useful for timing a peak and ensuring you are not going into a goal race overtrained. The estimated race times Strava generates from your recent activities use VO2 max estimates rather than Riegel's formula, which makes them a useful second opinion alongside a pure Riegel calculation.
5. McMillan Running Calculator
The McMillan calculator is a well-known training pace calculator that goes beyond basic Riegel predictions. It generates training pace recommendations for every zone -- easy, aerobic, long run, tempo, threshold, VO2 max, speed -- derived from a single input race time.
The strength of McMillan's approach is the specificity of the training zones and the way they relate to different types of workouts. A runner who wants to know exactly what pace to target in a 400m interval workout or a 3-mile tempo run can use the McMillan output as a starting point.
The McMillan calculator is free for basic predictions and is widely used in structured marathon training programs.
6. Your GPS Watch's Built-In Predictor
Most current GPS training watches include a race time predictor built into the firmware, typically derived from the watch's estimated VO2 max for your profile. Garmin, Polar, and COROS all offer this feature.
The advantage of the watch-based predictor is that it draws from your actual training data -- recent runs, heart rate data, pacing patterns -- rather than a single time trial result. This makes it potentially more accurate than a formula-based prediction, especially during a training block where you have not raced recently.
The limitation is opacity: the watch's prediction is a black box. You cannot tell whether it is accounting for recent fitness improvements, and the output does not include the split targets and pace zones you need for race-day planning.
Use the watch prediction as a reference and cross-check it against a Riegel formula prediction from your most recent race or time trial.
How These Tools Work Together
The most useful approach is to combine tools:
- Use a recent race result as input to the EvvyTools pace calculator or McMillan to generate predicted finish times and training pace zones
- Cross-check that prediction against your GPS watch's built-in estimate
- Use Runner's World resources to understand how training volume and conditions should adjust the raw prediction
- Use Strava's segment analysis to validate in training that you are hitting the pace zones you calculated
- On race day, use the cumulative split targets from the pace calculator to structure your pacing plan
No single tool does all of this. Together, they give you a data-based framework for training and racing that replaces "running by feel" with calibrated targets derived from your actual current fitness.
Creating a Pace Band for Race Day
Once you have a predicted finish time and target paces from any of these tools, the most practical race-day format is a pace band: a paper strip showing your cumulative split times at each mile or 5K marker.
For a 4:00 marathon running even splits (9:09/mile):
- Mile 5: 0:45:45
- Mile 10: 1:31:30
- Half marathon (13.1): 1:59:59
- Mile 18: 2:44:42
- Mile 20: 3:03:20
- Finish: 4:00:00
For a negative split version with a conservative first half (9:21/mi first half, 8:57/mi second half), each early milestone shifts by 10-15 seconds and the back-half markers accelerate. The EvvyTools pace calculator generates these cumulative splits as part of its output -- print the results before race day, cut the strip to wrist width, and you have a pace band that requires no battery, survives sweat and rain, and is readable with a single glance.
Most experienced coaches recommend the cumulative split format over per-mile pace alone because the arithmetic is done in advance rather than at mile 20 when mental resources are already under load. You check the cumulative time, compare it to the number on your band, and adjust pace accordingly -- no math required.
The Underlying Math
All of these tools, to varying degrees, build on Riegel's power law formula for race time prediction. Understanding the math -- what the 1.06 exponent represents, where the formula is most and least accurate, and how to adjust predictions for training volume and conditions -- makes you a better interpreter of any tool's output.
For a detailed breakdown of how Riegel's formula works and when to trust or adjust its predictions, read Riegel's Formula Explained: How Race Time Prediction Actually Works.
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