Sub-21 Minute 5K — Training Paces and Fitness Profile

Sub-21 sits between the recreational and competitive tiers — a marker of genuine aerobic development and structured training. Runners here typically have a solid base and at least one structured training phase under their belt.

Quick answer: To break Sub-21:00 in the 5K (RPI 47.1), your training paces are: easy 8:48/mi, threshold 7:03/mi, interval 6:10/mi. Equivalent fitness: Marathon 3:20:28, Half Marathon 1:36:22.

Training paces for Sub-21:00 5K

RPI 47.1 · Goal: 20:59 · All paces in min/mile

Easy (80%+ of weekly running)
8:48/mi5:28/km
Marathon Pace
7:29/mi4:39/km
Threshold (comfortably hard)
7:03/mi4:23/km
Interval (VO2max sessions)
6:10/mi3:50/km
Repetition (short fast reps)
5:43/mi3:33/km

Calculated from Daniels/Gilbert oxygen cost equations. Easy pace means "this pace or slower."

Equivalent race fitness

These are the predicted equivalent times at other distances for a runner with RPI 47.1 — assuming comparable training for each distance.

Marathon

3:20:28

7:39/mi

Half Marathon

1:36:22

7:21/mi

10K

43:30

7:00/mi

Training approach for Sub-21:00 5K

For sub-21 5K, the primary levers are VO2max development (interval training) and threshold stamina. Runners who plateau in the 21–23 minute range often lack sufficient interval training — they do plenty of easy running but not enough sessions at the aerobic ceiling. One interval session (800m–1000m repeats at interval pace) and one threshold session per week, supported by 30–45 miles of easy volume, drives consistent improvement toward this level.

Calculate your current training paces

The table above shows paces for Sub-21:00 5K fitness. Enter your current race time to see where you are now and how far from the goal you sit.

Training Pace Calculator

These paces are based on your race time — not your body

The Daniels/Gilbert formula predicts training zones from a single race result. StrideIQ goes further: it tracks how your body specifically responds to threshold and interval work — which sessions produce your biggest gains, how quickly you recover, and when your fitness is peaking. Population formulas start the conversation. Your individual response data finishes it.

Training pace tables →Start free trial

Common questions

What training paces are needed for sub-21 in the 5K?

For sub-21:00 (20:59): Easy 8:48/mi, Marathon 7:29/mi, Threshold 7:03/mi, Interval 6:10/mi, Repetition 5:43/mi. RPI 47.1. The key session for sub-21 is interval training at 6:10/mi — running at this pace raises the VO2max ceiling that determines how fast you can race.

What is the step from sub-25 to sub-21?

The gap between sub-25 and sub-21 typically closes in 12–24 months of consistent structured training. The shift from recreational to this level requires adding genuine interval work to a base of easy running and threshold sessions. Many runners make this jump by increasing weekly mileage to 35–45 miles and introducing weekly interval sessions for the first time.

What marathon time does sub-21 5K fitness predict?

Sub-21 5K fitness (RPI 47.1) projects to 3:20:28 marathon potential. This is a meaningful projection — if you have built marathon-specific training (long runs to 20 miles, marathon-pace work), this is the range you should target. Without long-run preparation, most runners with 21-minute 5K fitness underperform by 20–30 minutes in the marathon.

Other goal pace guides

Sub-20 Minute 5K →Sub-25 Minute 5K →Sub-40 Minute 10K →Sub-50 Minute 10K →Sub-2 Hour Half Marathon →Sub-4 Hour Marathon →Sub-17 Minute 5K →Sub-18 Minute 5K →Sub-19 Minute 5K →Sub-22 Minute 5K →Sub-23 Minute 5K →Sub-24 Minute 5K →Sub-27 Minute 5K →Sub-30 Minute 5K →Sub-35 Minute 10K →Sub-36 Minute 10K →Sub-37 Minute 10K →Sub-38 Minute 10K →Sub-39 Minute 10K →Sub-42 Minute 10K →Sub-45 Minute 10K →Sub-48 Minute 10K →Sub-55 Minute 10K →Sub-60 Minute 10K →Sub-1:15 Half Marathon →Sub-1:20 Half Marathon →Sub-1:25 Half Marathon →Sub-1:30 Half Marathon →Sub-1:35 Half Marathon →Sub-1:40 Half Marathon →Sub-1:45 Half Marathon →Sub-1:50 Half Marathon →Sub-2:30 Marathon →Sub-2:45 Marathon →Sub-3 Hour Marathon →Sub-3:05 Marathon →Sub-3:10 Marathon →Sub-3:15 Marathon →Sub-3:20 Marathon →Sub-3:30 Marathon →Sub-3:45 Marathon →Sub-4:30 Marathon →Sub-5 Hour Marathon →Training Pace Calculator →

Paces calculated using the Daniels/Gilbert oxygen cost equations (1979). All values derived from the same formula used by the StrideIQ training pace calculator. Goal times use the target-minus-one-second convention (e.g., sub-20 = 19:59 input).