[{"data":1,"prerenderedAt":723},["ShallowReactive",2],{"cheatsheet-\u002Fcheatsheets\u002Frace-time-prediction":3},{"id":4,"title":5,"body":6,"date":705,"dateModified":705,"description":706,"extension":707,"icon":708,"meta":709,"navigation":710,"path":711,"readTime":712,"seo":713,"sitemap":714,"stem":715,"tags":716,"version":721,"__hash__":722},"cheatsheets\u002Fcheatsheets\u002Frace-time-prediction.md","Race Time Prediction",{"type":7,"value":8,"toc":692},"minimark",[9,14,58,62,70,83,98,126,130,133,270,284,288,295,399,412,416,419,444,448,451,505,516,520,523,582,586,589,603,607,610,620,628,636,644,652,656,664],[10,11,13],"h2",{"id":12},"tldr","TL;DR",[15,16,19,42],"tldr-summary",{"lead":17,"takeaway":18},"One honest race result predicts your time at every other distance — the input matters more than the formula.","Garbage in, garbage out: a clean input race beats any amount of formula-tweaking.",[20,21,23],"template",{"v-slot:dos":22},"",[24,25,26,30,33,36,39],"ul",{},[27,28,29],"li",{},"Use a recent all-out race or time trial as the input",[27,31,32],{},"Predict between nearby distances (5K → 10K) for the tightest accuracy",[27,34,35],{},"Prefer a watch's running VO₂max over a lab number",[27,37,38],{},"Treat marathon predictions as a range, not a promise",[27,40,41],{},"Re-test every 6–8 weeks as fitness shifts",[20,43,44],{"v-slot:donts":22},[24,45,46,49,52,55],{},[27,47,48],{},"Don't extrapolate a 5K straight to marathon distance",[27,50,51],{},"Don't feed in a hot, hilly, or badly-paced effort",[27,53,54],{},"Don't trust a lab VO₂max reading over a real race result",[27,56,57],{},"Don't skip distance-specific training and expect the number to hold",[10,59,61],{"id":60},"what-race-time-prediction-actually-is","What race time prediction actually is",[63,64],"u-alert",{"color":65,"description":66,"icon":67,"title":68,"variant":69},"success","Race time prediction back-calculates a single fitness score — VDOT — from one race result, then projects it onto every other standard distance.","i-ph-check-circle-duotone","In one sentence","subtle",[71,72,73,74,78,79,82],"p",{},"A predictor doesn't measure your fitness directly — it reverse-engineers it from a performance you've already produced. The standard method, the ",[75,76,77],"strong",{},"Daniels-Gilbert formula",", converts a distance-and-time pair into ",[75,80,81],{},"VDOT",": a number that folds together both your aerobic ceiling and your running economy (how efficiently you convert oxygen into speed). Two runners can share an identical lab VO₂max and still post very different race times — the more economical runner has the higher VDOT, and the formula captures that automatically because it works from a real performance, not a treadmill reading.",[71,84,85,86,89,90,93,94,97],{},"That's also why the source of your VO₂max matters. A ",[75,87,88],{},"running watch estimate"," is distance-specific and tracks VDOT closely. A ",[75,91,92],{},"lab-measured VO₂max"," ignores economy entirely, so it typically reads ",[75,95,96],{},"5–10% higher"," than your true VDOT — plug it in and every predicted time comes out slightly optimistic.",[99,100,102,114,117],"callout",{"color":101},"neutral",[71,103,104],{},[105,106,113],"span",{"className":107},[108,109,110,111,112],"uppercase","text-xs","text-neutral-500","font-semibold","tracking-wider","How to read the impact scale",[115,116],"impact-scale",{},[71,118,119],{},[105,120,125],{"className":121},[122,123,124,110],"mt-3","block","text-sm","Ratings reflect how much each factor typically moves prediction accuracy. Individual results vary.",[10,127,129],{"id":128},"what-sharpens-the-prediction","What sharpens the prediction",[71,131,132],{},"Where accuracy actually comes from. Sorted roughly by how much each one moves the number.",[134,135,136,156],"table",{},[137,138,139],"thead",{},[140,141,142,146,149,153],"tr",{},[143,144,145],"th",{},"Factor",[143,147,148],{},"Why it helps",[143,150,152],{"align":151},"center","Impact",[143,154,155],{},"Best for",[157,158,159,184,201,217,235,252],"tbody",{},[140,160,161,167,175,181],{},[162,163,164],"td",{},[75,165,166],{},"A recent all-out race result",[162,168,169,170,174],{},"Captures fitness ",[171,172,173],"em",{},"and"," economy in one number — no separate formula guesses needed.",[162,176,177],{"align":151},[178,179],"impact-dots",{"value":180},"4",[162,182,183],{},"Any prediction",[140,185,186,191,194,198],{},[162,187,188],{},[75,189,190],{},"Predicting between nearby distances",[162,192,193],{},"5K → 10K keeps the extrapolation short; the %VO₂max gap between them is small.",[162,195,196],{"align":151},[178,197],{"value":180},[162,199,200],{},"3K–15K range",[140,202,203,208,211,215],{},[162,204,205],{},[75,206,207],{},"A flat, cool, honestly-paced input effort",[162,209,210],{},"The formula reads pace as pure effort — heat, hills, and uneven pacing all distort it.",[162,212,213],{"align":151},[178,214],{"value":180},[162,216,183],{},[140,218,219,224,227,232],{},[162,220,221],{},[75,222,223],{},"Training specifically for the target distance",[162,225,226],{},"The table assumes race-ready fitness at that distance; specific endurance work closes the gap.",[162,228,229],{"align":151},[178,230],{"value":231},"3",[162,233,234],{},"Half & marathon",[140,236,237,242,245,249],{},[162,238,239],{},[75,240,241],{},"A running watch's VO₂max estimate",[162,243,244],{},"Distance-specific and close to VDOT — a solid stand-in with no race on the calendar.",[162,246,247],{"align":151},[178,248],{"value":231},[162,250,251],{},"Quick estimates",[140,253,254,259,262,267],{},[162,255,256],{},[75,257,258],{},"Re-testing every 6–8 weeks",[162,260,261],{},"VDOT moves with training; a stale input race quietly drifts the whole table.",[162,263,264],{"align":151},[178,265],{"value":266},"2",[162,268,269],{},"Ongoing training",[271,272,274],"tip",{"icon":273},"i-ph-check-circle-fill",[71,275,276,279,280,283],{},[75,277,278],{},"The pattern:"," the single biggest lever is the ",[171,281,282],{},"quality of the input race"," — not which tool or formula you use. A clean, honest recent effort beats a lab test, a watch guess, or a PR from a year ago every time.",[10,285,287],{"id":286},"what-throws-it-off","What throws it off",[71,289,290,291,294],{},"The leaks. The ",[75,292,293],{},"cost"," column shows how much each one distorts the table, with the fix beside it.",[134,296,297,312],{},[137,298,299],{},[140,300,301,303,306,309],{},[143,302,145],{},[143,304,305],{},"What goes wrong",[143,307,308],{"align":151},"Cost",[143,310,311],{},"Fix",[157,313,314,331,348,365,382],{},[140,315,316,321,324,328],{},[162,317,318],{},[75,319,320],{},"Big distance gaps (5K → marathon)",[162,322,323],{},"Sustainable %VO₂max drops from ~95–97% at 5K to ~75–80% at marathon — a short race barely constrains the far end of that curve.",[162,325,326],{"align":151},[178,327],{"value":180,"tone":293},[162,329,330],{},"Anchor with a race or long tempo closer to your target distance.",[140,332,333,338,341,345],{},[162,334,335],{},[75,336,337],{},"Undertrained for the target distance",[162,339,340],{},"The table assumes matched training; a 5K specialist's marathon prediction ignores glycogen, fueling, and durability they haven't built.",[162,342,343],{"align":151},[178,344],{"value":180,"tone":293},[162,346,347],{},"Build distance-specific long runs and tempo work first.",[140,349,350,355,358,362],{},[162,351,352],{},[75,353,354],{},"A lab VO₂max as the input",[162,356,357],{},"Runs 5–10% above true VDOT because it ignores running economy — every prediction skews optimistic.",[162,359,360],{"align":151},[178,361],{"value":231,"tone":293},[162,363,364],{},"Use a watch estimate or a real race result instead.",[140,366,367,372,375,379],{},[162,368,369],{},[75,370,371],{},"A hilly, hot, or poorly-paced input race",[162,373,374],{},"Distorts the pace-to-effort mapping the whole formula depends on.",[162,376,377],{"align":151},[178,378],{"value":231,"tone":293},[162,380,381],{},"Re-test on a flat course in cool conditions, run evenly.",[140,383,384,389,392,396],{},[162,385,386],{},[75,387,388],{},"Treating the output as a guarantee",[162,390,391],{},"Pacing discipline and fueling execution on race day still decide the actual result.",[162,393,394],{"align":151},[178,395],{"value":266,"tone":293},[162,397,398],{},"Use the prediction as a target range, not a promise.",[400,401,403],"warning",{"icon":402},"i-ph-warning",[71,404,405,407,408,411],{},[75,406,278],{}," almost every distortion traces back to a bad ",[171,409,410],{},"input",", not a bad formula. Fix what you feed it before you doubt the number it gives back.",[10,413,415],{"id":414},"three-ways-to-get-your-starting-number","Three ways to get your starting number",[71,417,418],{},"You don't need a race on the calendar to start. Pick whichever is available.",[420,421,422,430,437],"card-group",{},[423,424,427],"training-card",{"badges":425,"title":426,"value":180},"Most accurate,Any distance","Recent race result",[71,428,429],{},"A race you ran hard in recent weeks, close to full effort. The gold-standard input — it captures real fitness and economy together, with no estimation step.",[423,431,434],{"badges":432,"title":433,"value":180},"No race needed,Self-timed","All-out time trial",[71,435,436],{},"Nothing on the calendar? A genuine all-out effort over a known distance, ideally 3K–10K on a flat, honest course, works just as well.",[423,438,441],{"badges":439,"title":440,"value":231},"Instant,Slightly optimistic","Watch VO₂max",[71,442,443],{},"Running-specific watch estimates track VDOT closely. Skip a lab VO₂max here — it reads 5–10% high and will over-predict every distance.",[10,445,447],{"id":446},"how-far-you-can-trust-it","How far you can trust it",[71,449,450],{},"Every prediction ships with a margin, and it widens with distance — pacing, fueling, and glycogen management add variability a formula alone can't capture.",[134,452,453,463],{},[137,454,455],{},[140,456,457,460],{},[143,458,459],{},"Distance",[143,461,462],{"align":151},"Prediction margin",[157,464,465,473,481,489,497],{},[140,466,467,470],{},[162,468,469],{},"1K",[162,471,472],{"align":151},"± 3%",[140,474,475,478],{},[162,476,477],{},"3K – 10K",[162,479,480],{"align":151},"± 2.5%",[140,482,483,486],{},[162,484,485],{},"15K",[162,487,488],{"align":151},"± 3.5%",[140,490,491,494],{},[162,492,493],{},"Half Marathon",[162,495,496],{"align":151},"± 4%",[140,498,499,502],{},[162,500,501],{},"Marathon",[162,503,504],{"align":151},"± 5.5%",[506,507,509],"note",{"icon":508},"i-ph-target",[71,510,511,512,515],{},"Read the marathon figure as a ",[75,513,514],{},"range",", not a single number — at ±5.5%, a 3:30 prediction really means \"roughly 3:19 to 3:41\" depending on how well you execute the parts a formula can't see: pacing, fueling, and the last 10K.",[10,517,519],{"id":518},"which-tool-answers-which-question","Which tool answers which question",[71,521,522],{},"Four tools cover this territory, and it's easy to reach for the wrong one.",[134,524,525,535],{},[137,526,527],{},[140,528,529,532],{},[143,530,531],{},"Question",[143,533,534],{},"Tool",[157,536,537,549,560,571],{},[140,538,539,542],{},[162,540,541],{},"What time could I run at another distance?",[162,543,544],{},[545,546,548],"a",{"href":547},"\u002Ftools\u002Frace-time-predictor","Race Time Predictor",[140,550,551,554],{},[162,552,553],{},"What pace should today's easy, threshold, or interval run be?",[162,555,556],{},[545,557,559],{"href":558},"\u002Ftools\u002Ftraining-pace-calculator","Training Pace Calculator",[140,561,562,565],{},[162,563,564],{},"How do I manually plan my own pacing splits for a race?",[162,566,567],{},[545,568,570],{"href":569},"\u002Ftools\u002Frace-pace-calculator","Race Pace Calculator",[140,572,573,576],{},[162,574,575],{},"How should my splits look based on my actual fitness?",[162,577,578],{},[545,579,581],{"href":580},"\u002Ftools\u002Frace-strategy-calculator","Race Strategy Calculator",[10,583,585],{"id":584},"how-to-track-it","How to track it",[71,587,588],{},"A single prediction is a snapshot, not a trend. What actually matters is whether your VDOT is climbing.",[271,590,592],{"icon":591},"i-ph-trend-up",[71,593,594,595,597,598,602],{},"Re-run the ",[545,596,548],{"href":547}," every 6–8 weeks from a fresh race or time trial, and let the ",[545,599,601],{"href":600},"\u002F","Runima app"," track the trend automatically from your uploaded activities — a rising VDOT over months is worth more than any single predicted time.",[10,604,606],{"id":605},"common-mistakes","Common mistakes",[71,608,609],{},"The traps that quietly wreck an otherwise sound prediction.",[611,612,614],"caution",{"icon":613},"i-ph-warning-circle",[71,615,616,619],{},[75,617,618],{},"Extrapolating a 5K straight to marathon distance."," The %VO₂max gap between them is too wide for a short race to constrain — anchor with something closer to 42.2K first.",[611,621,622],{"icon":613},[71,623,624,627],{},[75,625,626],{},"Feeding in a lab VO₂max."," It ignores running economy and reads 5–10% high, so every distance comes out optimistic. Use a watch estimate or a real race instead.",[611,629,630],{"icon":613},[71,631,632,635],{},[75,633,634],{},"Using an old PR as if it were current fitness."," VDOT drifts with training load — a result from a year ago describes a runner you no longer are.",[611,637,638],{"icon":613},[71,639,640,643],{},[75,641,642],{},"Ignoring race-day execution."," Pacing discipline and fueling decide how close you land to the number — a formula can't run the race for you.",[611,645,646],{"icon":613},[71,647,648,651],{},[75,649,650],{},"Trusting a hilly or overheated input race."," Conditions distort the pace-to-effort mapping the whole prediction depends on. Re-test somewhere flat and cool.",[10,653,655],{"id":654},"go-deeper","Go deeper",[71,657,658,659,663],{},"There's no single deep-dive article for this one yet — the full methodology lives on the ",[545,660,661],{"href":547},[75,662,548],{}," itself.",[99,665,668],{"color":666,"icon":667},"primary","i-ph-books",[71,669,670,671,677,678,684,685,691],{},"For the training-zone math these predictions feed into, see ",[545,672,674],{"href":673},"\u002Fblog\u002Ftraining-paces",[75,675,676],{},"Training Paces: Science and Calculation",". For why raw VO₂max doesn't decide race day on its own, see ",[545,679,681],{"href":680},"\u002Fblog\u002Fthe-vo2max-trap",[75,682,683],{},"The VO₂max Trap"," and ",[545,686,688],{"href":687},"\u002Fblog\u002Frunning-economy",[75,689,690],{},"Running Economy",".",{"title":22,"searchDepth":693,"depth":693,"links":694},2,[695,696,697,698,699,700,701,702,703,704],{"id":12,"depth":693,"text":13},{"id":60,"depth":693,"text":61},{"id":128,"depth":693,"text":129},{"id":286,"depth":693,"text":287},{"id":414,"depth":693,"text":415},{"id":446,"depth":693,"text":447},{"id":518,"depth":693,"text":519},{"id":584,"depth":693,"text":585},{"id":605,"depth":693,"text":606},{"id":654,"depth":693,"text":655},"2026-07-04T12:00:00","Your quick, science-backed guide to race time prediction — how VDOT turns one race result into finish times at every distance, and when to trust the number.","md","i-ph-flag-checkered",{},true,"\u002Fcheatsheets\u002Frace-time-prediction","6 min read",{"title":5,"description":706},{"loc":711},"cheatsheets\u002Frace-time-prediction",[717,718,719,720],"running","race-time-prediction","vdot","pacing","v1.0","aXxZbVKZ-cAGNxnkzCLo4JsyEQN7gQ_lK8GaC8vwpCY",1784124159547]