Question 1

How accurate is the Riegel formula for a marathon?

Accepted Answer

Riegel predictions are ±2–3% for half marathon and ±5 minutes for full marathon in the 3:00–4:30 finish range. A 10K input gives a tighter prediction than a 5K input, and you should factor in training volume, course profile, and weather.

Question 2

Should I use my 5K or 10K as the input?

Accepted Answer

Use the race that is closest in distance to your target. For a marathon goal, 10K or half marathon inputs produce the most reliable prediction. A 5K extrapolation tends to overestimate marathon fitness because it does not capture endurance.

Question 3

What is a negative split and why use it?

Accepted Answer

A negative split runs the second half of the race faster than the first. Most elite marathon world records (and many Boston champions of the past decade) used negative splits because they reduce early lactate buildup and save glycogen for the final 10K.

Question 4

What is VDOT exactly?

Accepted Answer

VDOT is a number Jack Daniels derived from race performance that approximates VO₂max adjusted for running economy. Higher VDOT = better runner. We show an estimate from your 5K prediction — a VDOT of 50 roughly equals a 19:57 5K.

Question 5

How do the Easy / Marathon / Threshold / Interval zones differ?

Accepted Answer

Easy = conversational aerobic base (long runs, recovery). Marathon = sustainable hard effort for 2–4 hours. Threshold = 20–40 min continuous or "cruise intervals" at lactate threshold. Interval = 3–5 min reps at VO₂max.

Question 6

Should I train at race pace every week?

Accepted Answer

No. Around 80% of weekly volume should be Easy. Race-pace work is reserved for goal marathon tune-ups or half-marathon specific sessions. Over-training at race pace is the top cause of plateau and injury for recreational runners.

Question 7

What are heart-rate zones (Karvonen)?

Accepted Answer

Karvonen defines zones as (HRmax − HRrest) × target% + HRrest. It individualizes HR zones using your resting HR. Our pace zones use rough HRmax percentages; for precise HR training, measure resting HR first thing in the morning for 5–7 days and use a Karvonen calculator.

Question 8

Why is my target time different from the prediction?

Accepted Answer

The prediction comes from Riegel and assumes equal effort at both distances. Your personal goal can differ if you are training specifically for this distance, expect hills, heat, or simply want a stretch goal. Entering a target time recomputes the split card around your chosen time.

Question 9

Can I trust the predictions if I am a beginner?

Accepted Answer

Predictions assume consistent training and that your input race was an all-out effort. If you ran your 5K jogging with a friend, the marathon prediction will be too optimistic. Re-run a time trial every 6–8 weeks for a realistic baseline.

Question 10

How should pace change on hilly courses?

Accepted Answer

A common rule: +5–10 sec/km for every 1% uphill gradient, −3–5 sec/km per 1% downhill (up to −10 sec/km before you lose efficiency). Chuncheon and Dong-A Marathons are relatively flat; JTBC Seoul has rolling hills in the final 10K.

Question 11

Do I need to train in mile units?

Accepted Answer

No. The km/mile toggle is purely for display preference. Korean runners typically train in km and Americans in miles. Elite training plans mix both — what matters is consistent effort, not the unit label.

Question 12

Why does my watch predict different times?

Accepted Answer

Garmin and Apple Watch use VO₂max estimates from HR + pace telemetry over many runs. Our calculator uses only one finish time + Riegel. Watches capture recent fitness trends, but overestimate if you did a lot of easy running without tempo/LT sessions.

Question 13

Should I pick an aggressive or safe target?

Accepted Answer

For first-time marathoners: match the Riegel prediction and target a negative −2% split. For experienced runners targeting a PR: choose a time 1–2% faster than the prediction if your long-run pace work is solid. Avoid going 3%+ beyond prediction.

Question 14

How do I cut the printed wrist band?

Accepted Answer

Print on regular A4 paper in landscape orientation. Cut along the dashed border into a single horizontal strip, fold once lengthwise for rigidity, and secure around the wrist with clear tape or a small safety pin.

Question 15

Is this tool free forever?

Accepted Answer

Yes. Race Pace Calculator is free and runs entirely in your browser — no accounts, no data uploaded anywhere. Ads support ongoing maintenance.

FAQ