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Sub-4:00 is the most commonly cited marathon goal in recreational running. It requires real endurance, consistent volume over months, smart pacing on race day, and honest easy-day discipline. The training paces here represent what a genuine sub-4 marathoner actually runs during their training cycle.
Quick answer: To break Sub-4:00:00 in the Marathon (RPI 37.9), your training paces are: easy 10:11/mi, threshold 8:32/mi, interval 7:50/mi. Equivalent fitness: Half Marathon 1:56:07, 10K 52:22.
RPI 37.9 · Goal: 3:59:59 · All paces in min/mile
Calculated from StrideIQ's RPI equations. Easy pace means "this pace or slower."
These are the predicted equivalent times at other distances for a runner with RPI 37.9 — assuming comparable training for each distance.
Half Marathon
1:56:07
8:51/mi
10K
52:22
8:26/mi
5K
25:14
8:07/mi
For sub-4 marathon, marathon-pace runs and long runs at easy pace are the two most critical training elements. Marathon-pace work — running the final miles of a long run at goal pace — teaches your body to maintain effort when glycogen is depleted, which is exactly what the final 10K of the marathon demands. Easy running makes up 80% or more of weekly volume and builds the aerobic base and fat-oxidation capacity that sustains marathon effort for hours. Threshold running matters, but marathon pace and easy base are the top priorities.
To train for a sub-4:00:00 marathon (3:59:59), your training zones are: Easy 10:11/mi, Marathon 9:09/mi, Threshold 8:32/mi, Interval 7:50/mi, Repetition 7:26/mi. Your marathon-pace training runs target 9:09/mi — your long run easy days should be at 10:11 or slower. The gap between these paces is deliberate: different adaptations, different sessions.
Going out too fast on race day, and running easy training days at marathon pace. Both errors stem from the same cause: underestimating how much the marathon punishes pace that feels "comfortable" early. Easy training pace for a sub-4 runner (10:11/mi or slower) often feels almost embarrassingly slow. But running easy days at marathon pace leaves no adaptation reserve for the quality sessions that build fitness. And starting a marathon at a pace that feels good virtually guarantees a painful final 10K.
Sub-4:00 marathon fitness (RPI 37.9) projects to approximately 1:56:07 for the half marathon — assuming comparable training for the half distance. Because the half marathon is run at a higher percentage of VO2max than the marathon, runners who are specifically marathon-trained (high volume, long runs, marathon-pace work) may underperform their half marathon equivalent until they do more half-specific work. The equivalency reflects aerobic capacity, not single-distance peaking.
Paces calculated using StrideIQ's RPI equations. 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).