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Interval Training Calculator

Calculate target interval paces from your race times using Daniels VDOT

400m I Pace

1:27

VDOT

47

800m

2:54

200m

0:40

hrs

:

min

:

sec

Your Estimated VDOT

47

Daniels Running Fitness Index

Target Interval Paces

200m0:40
Rest: 1:592-3 x 4-6
400m1:27
Rest: 2:541-2 x 4-8
800m2:54
Rest: 2:544-10 reps
1600m5:47
Rest: 2:543-5 reps

Yasso 800s Prediction

2:54

800m target time. If you can run 10 × 800m at this pace, your predicted marathon time matches hours:minutes.

Sample Workouts

VO2max Builder

5 × 1000m at 3:37 w/ 3 min jog

Speed Session

8 × 400m at 1:27 w/ 2:54 rest

Yasso 800s

10 × 800m at 2:54 w/ 2:54 jog

Frequently Asked Questions

Q

How are interval training paces calculated from race times?

Interval paces are derived from your VO2max (estimated from race times via the Daniels VDOT table). Your VO2max pace (I pace) is approximately 95-100% of VO2max. For 400m repeats, target 3-5% faster than 5K pace. For 800m repeats, target 5K pace minus 5-10 sec/400m.

  • VDOT is estimated from your best recent race time
  • I (Interval) pace = approximately 95-100% VO2max effort
  • R (Repetition) pace = faster, works neuromuscular speed
  • T (Threshold) pace = slower, improves lactate clearance
  • 400m target: roughly your 5K pace minus 5 sec per 400m
  • 800m target (Yasso): marathon time in hours:min = 800m in min:sec
Training Zone% VO2maxEffort LevelTypical Duration
E (Easy)59-74%Conversational30-150 min
T (Threshold)83-88%Comfortably hard20-40 min
I (Interval)95-100%Hard, controlled3-5 min reps
R (Repetition)105-120%Near sprint30-90 sec reps
Q

What is the Yasso 800s method?

Yasso 800s predict marathon time: if you can run 10 x 800m in X minutes and Y seconds, your marathon time is approximately X hours and Y minutes. Example: 10 x 800m in 3:30 each predicts a 3:30 marathon. This is a rough correlation, not an exact prediction.

  • Run 10 x 800m with equal rest (jog 400m between reps)
  • Average 800m time in min:sec = marathon time in hrs:min
  • 3:00 per 800m = ~3:00 marathon
  • 3:30 per 800m = ~3:30 marathon
  • 4:00 per 800m = ~4:00 marathon
  • Build up to 10 reps over several weeks (start with 4-5)
800m TimePredicted Marathon5K EquivalentVDOT
2:452:45:0017:3058
3:003:00:0019:1553
3:303:30:0022:3046
4:004:00:0026:0040
4:304:30:0029:4535
Q

What is the optimal work-to-rest ratio for intervals?

It depends on the interval distance and training goal. For VO2max intervals (800-1600m): 1:1 work-to-rest ratio. For speed work (200-400m): 1:2 to 1:3 work-to-rest. For threshold intervals (mile repeats): 1:0.25 rest (short recovery). Rest can be standing, walking, or jogging.

  • 200m repeats: 1:3 ratio (e.g., 35 sec work, 105 sec rest)
  • 400m repeats: 1:2 ratio (e.g., 75 sec work, 150 sec rest)
  • 800m repeats: 1:1 ratio (e.g., 3:00 work, 3:00 jog)
  • 1600m repeats: 1:0.5 to 1:1 ratio
  • Threshold intervals: 1:0.2 ratio (e.g., 5:00 work, 1:00 rest)
DistanceWork:RestRest TypeSets × Reps
200m1:3Walk/stand 200m2-3 × 4-6
400m1:2Jog 200-400m1-2 × 4-8
800m1:1Jog 400m4-10 reps
1600m1:0.5Jog 400m3-5 reps
Q

How does VDOT relate to VO2max?

VDOT is Jack Daniels' running-specific fitness metric. It correlates with but is not identical to lab-measured VO2max. VDOT accounts for running economy in addition to aerobic capacity. A higher VDOT means faster equivalent race times across all distances.

  • VDOT 30: beginner (5K in ~30:40, marathon in ~4:49)
  • VDOT 40: recreational (5K in ~22:15, marathon in ~3:35)
  • VDOT 50: competitive (5K in ~17:35, marathon in ~2:55)
  • VDOT 60: advanced (5K in ~14:53, marathon in ~2:27)
  • VDOT 70+: elite (5K in ~13:06, marathon in ~2:10)
VDOT5K Time10K TimeMarathon Time
3526:1054:254:12:00
4022:1546:153:35:00
4519:2040:153:07:00
5017:0535:352:45:00
5515:1531:452:28:00
Q

How many interval sessions should I do per week?

Most runners benefit from 1-2 quality sessions per week: one interval/speed session and one tempo session. The remaining runs should be easy (80/20 rule). Beginners: start with 1 quality session. Advanced runners can handle 3 quality sessions if total volume supports it.

  • Beginner (< 25 mi/week): 1 quality session max
  • Intermediate (25-40 mi/week): 1 interval + 1 tempo
  • Advanced (40-60 mi/week): 2 quality + 1 long run
  • Elite (60+ mi/week): 2-3 quality sessions
  • Never do hard sessions on consecutive days
  • Easy days should feel genuinely easy (can hold conversation)

Example Calculations

15K Runner (20:00) Planning 400m Repeats

Inputs

Race Distance5K
Race Time20:00
Interval Distance400m

Result

400m Target Pace1:28
Estimated VDOT45
200m Pace0:41
800m Pace3:02
1600m Pace6:20
Rest (400m, 1:2)2:56

A 20:00 5K corresponds to approximately VDOT 45. The Daniels I pace for VDOT 45 is about 88 sec per 400m = 1:28. With a 1:2 work-to-rest ratio: rest = 88 × 2 = 176 sec = 2:56.

2Marathon Runner (3:30) Using Yasso 800s

Inputs

Race DistanceMarathon
Race Time3:30:00
Interval Distance800m

Result

800m Target Pace3:30
Estimated VDOT46
400m Pace1:42
Rest (800m, 1:1)3:30
Workout10 x 800m

Yasso 800s method: 3:30 marathon target = 3:30 per 800m. With 1:1 work-to-rest: jog 400m in approximately 3:30. Build from 4 reps up to 10 reps over 6-8 weeks.

310K Runner (45:00) Planning 1600m Repeats

Inputs

Race Distance10K
Race Time45:00
Interval Distance1600m

Result

1600m Target Pace6:10
Estimated VDOT43
400m Pace1:30
800m Pace3:05
Rest (1600m, 1:0.5)3:05
Suggested Workout4 x 1600m

A 45:00 10K corresponds to approximately VDOT 43. The I pace per 400m is about 90-92 sec. For 1600m: 4 × 92 = 368 sec = 6:08, rounded to 6:10. Rest at 1:0.5 ratio = 368 × 0.5 = 184 sec = 3:04, rounded to 3:05.

Formulas Used

VDOT Estimation from Race Time

VDOT ≈ -4.6 + 0.182258 × (D/T) + 0.000104 × (D/T)²

Simplified Daniels formula estimating VDOT from race performance. The full model uses oxygen cost and VO2 fraction curves.

Where:

D= Race distance in meters
T= Race time in minutes
VDOT= Daniels running fitness index (unitless)

Interval Pace from VDOT

I Pace (sec/400m) ≈ (-4.511 + 0.7907 × VDOT) / VDOT × correction

Approximation of Daniels I pace. In practice, paces are looked up from the VDOT table.

Where:

VDOT= Daniels fitness index derived from race time
I Pace= Target interval pace for 3-5 minute efforts
correction= Distance-specific adjustment factor

Rest Period Calculation

Rest (sec) = Work Time (sec) × Work:Rest Ratio

Determines recovery time between interval repetitions.

Where:

Work Time= Duration of one interval repetition in seconds
Work:Rest Ratio= Ratio factor (1.0 for 1:1, 2.0 for 1:2, etc.)

Understanding Interval Training Paces

1

VDOT and How It Determines Training Paces

VDOT 45 – corresponding to a 20:00 5K or a 41:30 10K – is the threshold where recreational runners transition into competitive territory. At this fitness level, your 400m interval pace (I pace) is approximately 88 seconds, and your 800m pace is 3:02. These paces target 95–100% of VO2max, the intensity that maximally stresses the cardiovascular system without crossing into anaerobic collapse.

The Daniels VDOT table maps every fitness level to five precise training paces. A VDOT 40 runner (22:15 5K) runs 400m intervals at 96 seconds; a VDOT 55 runner (15:15 5K) runs them at 72 seconds. The difference is not arbitrary – each pace represents the same 95–100% VO2max effort relative to the runner’s current fitness. Running intervals faster than your VDOT prescribes does not produce better adaptation; it shifts the stimulus toward anaerobic glycolysis and increases injury risk.

To find your VDOT, enter your most recent race time from the past 6–8 weeks. A stale result (3+ months old) likely underestimates your current fitness if you have been training consistently. Conversely, a race time set during a taper peak may overestimate daily training fitness by 2–3% – use the next-lower VDOT for interval sessions to avoid overreaching.

I pace from Daniels Running Formula lookup tables
VDOT5K Equiv.400m I Pace800m I Pace1600m I Pace
3526:101:523:507:55
4022:151:363:186:50
4519:201:283:026:20
5017:051:202:465:48
5515:151:122:325:18
2

Work-to-Rest Ratios and Recovery Programming

The recovery interval between hard repetitions is just as important as the work interval. Too little rest and you cannot sustain the target pace; too much rest and you lose the accumulated VO2max stimulus. The Daniels system prescribes specific work-to-rest ratios by interval distance: 200m repeats use 1:3, 400m use 1:2, 800m use 1:1, and 1600m use 1:0.5.

For a VDOT 45 runner doing 6 × 400m at 88 seconds each: the rest interval at 1:2 is 176 seconds (2:56) of jogging between reps. Total session time is (6 × 88) + (5 × 176) = 528 + 880 = 1,408 seconds (23:28) of quality work plus recovery. Adding a 15-minute warm-up and 10-minute cool-down, the full workout runs approximately 48 minutes.

Recovery can be standing, walking, or light jogging. Jogging is preferred for 800m and 1600m intervals because it keeps the cardiovascular system partially elevated, reducing the VO2 "ramp-up" time for the next repetition. For shorter 200m repeats, standing or walking recovery is acceptable because the work interval is too short to sustain peak VO2.

Interval DistanceWork:RestExample (VDOT 45)Rest Activity
200m1:341s work / 123s restWalk or stand
400m1:288s work / 176s restJog 200–400m
800m1:13:02 work / 3:02 restJog 400m
1600m1:0.56:20 work / 3:10 restJog 400m
3

Yasso 800s and Marathon-Specific Intervals

Yasso 800s are the most widely known marathon-specific interval workout: run 10 × 800m where your target 800m time in minutes:seconds equals your marathon target in hours:minutes. Aiming for a 3:45 marathon? Run 800s in 3:45 each. The correlation is empirical rather than physiological – it works because the required VO2max for both efforts is similar.

Build up to the full 10 repetitions over 6–8 weeks. Start with 4–5 reps at target pace in week 1, add 1 rep per week, and reach 10 reps 3–4 weeks before race day. The rest between reps is a 400m jog at approximately the same duration as the work interval (1:1 ratio). If you cannot maintain the target pace by rep 8, your marathon goal may be too aggressive.

Yasso 800s are a rough correlation, not a precise prediction. Runners with high speed but low endurance may hit 3:15 per 800m but run a 3:35 marathon because they lack the long-run base for the final 10K. Combine Yasso results with a half marathon race time and the race predictor calculator for a more reliable marathon projection. Use the tempo run pace calculator to build the threshold foundation that supports marathon-pace endurance.

Never do a Yasso 800 workout in the final 10 days before a marathon. The session creates significant muscle damage that takes 7–10 days to fully repair. Schedule the last Yasso session 2–3 weeks pre-race.

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Last Updated: Mar 25, 2026

This calculator is provided for informational and educational purposes only. Results are estimates and should not be considered professional financial, medical, legal, or other advice. Always consult a qualified professional before making important decisions. UseCalcPro is not responsible for any actions taken based on calculator results.

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