Acute:chronic workload ratio calculator
Is this week a sensible step up, or a spike? Compare it with your last four weeks, the way sports scientists track training load, and see the 10% rule next to it.
Previous four weeks (km), oldest first
Four-week average: 31.0 km. Steady range this week: 25–40 km. The 10% rule from last week would cap you at 37.4 km.
Fitness is built on what you’re used to
Your body adapts to the load of recent weeks. The shaded band is 0.8–1.3 times that average. Drag this week’s distance above and watch where it lands: the same 40 km can be routine for one runner and a spike for another.
How to read your ratio
The ratio divides this week’s distance (acute load) by the average of the previous four weeks (chronic load). Under 0.8 you’re doing less than usual, which is fine for a recovery week or taper. Between 0.8 and 1.3 you’re building steadily. Above 1.5 you’re asking your tendons and bones to absorb a jump they haven’t adapted to yet; that’s when many overuse injuries appear.
These thresholds come from team-sport research led by Tim Gabbett and have been debated since, so use the number as a nudge rather than a verdict. The 10% rule is similar in spirit and similarly approximate. Build a few weeks, then hold or drop back for a week before building again. Log every run in your running log and this page fills in your weeks automatically.
Questions runners ask
What is the acute:chronic workload ratio?
It compares what you did this week (acute load) with your average week over the last four (chronic load). A ratio of 1.0 means this week matches your recent normal; 1.5 means it’s 50% bigger.
What is a safe ACWR for runners?
Sports scientist Tim Gabbett’s work (British Journal of Sports Medicine, 2016) described 0.8–1.3 as a “sweet spot” and ratios above 1.5 as a period of higher injury risk. Later research has questioned how precise these thresholds are, so treat them as a prompt to think, not a rule.
What is the 10% rule in running?
A long-standing coaching guideline: don’t raise weekly mileage by more than about 10% from one week to the next. It isn’t strongly supported as an exact number, but it pushes runners toward gradual build-ups, which is the point.
Should I use distance or time as load?
Either works if you’re consistent. This page uses distance. Time × effort (session RPE) is more complete when you mix hills, trails and speed work.