VDOT Training Guide: How to Use Jack Daniels' Formula for Real Speed

If you've ever stared at a training plan that said 'run 8 x 800m at I pace' and thought 'what the hell is I pace,' you're not alone. The five letters — E, M, T, I, R — are the foundation of Jack Daniels' VDOT system, and they're the most precise way to prescribe running intensity ever published. This guide explains what VDOT actually is, how to find yours, and exactly how fast each zone should feel.

What is VDOT?

VDOT is Jack Daniels' shorthand for a pseudo-VO2max score derived from race performance. Real VO2max requires a lab, a mask, and a treadmill that hurts. VDOT skips all that: you plug in a recent race time, and the formula returns a single number that captures your current aerobic fitness. From that number, every training pace falls out automatically.

The genius of the system is that it normalises ability. A 50-VDOT athlete and a 70-VDOT athlete don't share workouts in absolute pace, but they share workouts in relative effort. T pace for both is the same physiologically — they're just running it at different clock times.

How to calculate your VDOT

The cleanest input is a hard, recent (within 6 weeks) race effort over 1500m–half marathon distance. A workout time-trial works in a pinch but tends to under-read. Punch your time into a VDOT calculator and read the number — that's it.

• 5K is the gold standard input — long enough to be aerobic, short enough that pacing errors don't dominate
• Half marathon works if you've raced it recently and weren't fading by mile 10
• Avoid marathons for VDOT — fueling and heat throw off the read
• Avoid 1 mile / 1500m unless you have real speed — anaerobic contribution skews the formula high

The five training paces

E — Easy pace (recovery + base)

About 65–79% of VO2max, conversational, heart rate 65–75% max. This is the most-run pace in any well-built program. E pace builds capillary density, mitochondria, and connective-tissue durability. If you're gasping on easy days, you're sacrificing the engine you need to race.

M — Marathon pace

Roughly 80–85% of VO2max. Tempo-adjacent but more sustainable. Used in marathon-specific workouts — 2 × 4mi at M, 16 mile long runs with a 10mi M finish. For non-marathoners, M pace is a 'comfortably hard' aerobic effort.

T — Threshold pace

About 86–88% of VO2max — the pace you could hold for roughly an hour in a race. Often called 'comfortably hard.' Workouts: 4 × 1mi at T with 1' jog, or 20–30' continuous tempo. T work raises your lactate threshold — the single biggest determinant of distance performance.

I — Interval pace

Roughly your current 3K–5K race pace, or about 95–100% of VO2max. Workouts: 5 × 1000m at I with 3' jog, or 6 × 800m. Reps last 3–5 minutes — long enough to fully tax VO2max. This is the pace that raises your aerobic ceiling.

R — Repetition pace

Roughly mile race pace, with very long recoveries (1:2 work:rest or more). Workouts: 8 × 400m at R with 400m jog. Builds running economy, speed, and mechanics — not aerobic capacity. Often neglected by adults; that's why so many feel 'one-paced.'

How much time at each pace?

A typical 50-mile week for a 1:30 half-marathoner might look like: 80% E (40 miles), 8% M (4 miles), 6% T (3 miles), 4% I (2 miles), 2% R (1 mile). The polarized shape — lots of easy, a little hard, almost nothing in the moderate middle — is consistent across the research and across coaching practice.

Most amateurs train too hard on easy days and too easy on hard days. VDOT is the simplest way to stop doing both.

Common mistakes

• Using a stale race time. Your VDOT today is not your VDOT from a year ago — recalculate after every race.
• Bumping VDOT mid-cycle because a workout 'felt easy.' Workouts feel easy in week 6 of a build. Wait for the race.
• Running E pace too fast. If your easy day pace is within 30 seconds of your T pace, you're not building base.
• Skipping R entirely. Even marathoners benefit from a small dose — it preserves leg speed and mechanics.

How to apply VDOT to your training week

1. 01Race a 5K or recent hard workout, plug into the calculator, lock in your VDOT
2. 02Print your five paces and tape them on the fridge — no guessing on workout day
3. 03Build 80% of weekly volume at E, 1–2 quality sessions at T or I, optional R touch every 7–10 days
4. 04Re-test every 6–10 weeks; expect 1–3 VDOT points per build if you're training honestly