Performance
ACWR Calculator — Acute:Chronic Workload Ratio for Runners
Compare this week's training load against your previous three weeks to spot an unintended ramp. Reports the uncoupled ratio, which avoids the statistical artefact in the original formula.
A 60 min run at RPE 6 = 360. Any unit works — use the same one for all four weeks.
A moderate step up. Worth holding here for a week rather than adding again.
The coupled form divides this week by an average that still contains this week. It is the original formulation and what most calculators report, but the shared term pulls the ratio toward 1.0 and creates a statistical artefact. The headline figure above excludes the current week for that reason.
ACWR is a load-spike flag, not an injury prediction. The thresholds are population averages and the metric is actively disputed in the literature. Use it to notice a jump you did not intend, alongside how you actually feel, sleep and recover.
What the ratio is
The acute:chronic workload ratio divides this week's training load by your average weekly load over the preceding block. A ratio near 1.0 means this week looks like your recent normal. A ratio of 1.6 means you did roughly 60% more than you have been used to.
The number is unit-agnostic. Session RPE (rating of perceived exertion multiplied by minutes) is the most practical for runners, but kilometres, minutes or TSS all work provided you use the same unit for every week.
Coupled versus uncoupled — why this page reports the second one
The original formulation divides the acute week by an average that **includes that same week**. Lolli and colleagues showed in 2017 that this shared term creates mathematical coupling: the acute load appears on both sides of the division, which drags the ratio toward 1.0 and generates correlation with injury that is partly a statistical artefact rather than a real signal.
The uncoupled form excludes the current week from the chronic average. This page leads with that figure and shows the coupled one underneath for comparison, because most calculators report the coupled number without saying which form they used.
How much confidence the thresholds deserve
Honestly: less than the way they are usually presented.
The 0.8 to 1.3 "sweet spot" comes from Gabbett's work in team sports. A 2025 systematic review and meta-analysis of 22 cohort studies did find ratios above 1.5 associated with higher injury rates, and the IOC consensus still includes ACWR in load monitoring. But Impellizzeri and colleagues have set out substantial conceptual problems — the time windows have no physiological justification, the metric captures training load rather than tissue loading, and results across meta-analyses have been inconsistent. One 2020 paper argued directly for dismissing the ratio and its underlying theory.
The defensible position is that ACWR is a **crude heuristic for noticing load spikes**, not a predictive model. A high ratio is a prompt to look at your week, not a diagnosis. Treat a reading alongside sleep, soreness, and whether the jump was planned.
Using it sensibly
- Ratios naturally swing when your baseline is low. Coming back from two easy
- A deliberate build week above 1.3 is not automatically a problem. An
- The metric says nothing about *what* you did. Adding 40% more easy volume
- If you want to know whether you are rested enough to race rather than
Frequently Asked Questions
What is a safe ACWR?
The commonly cited range is 0.8 to 1.3, with ratios above 1.5 associated with raised injury rates in a 2025 meta-analysis of 22 cohort studies. Treat these as population averages rather than personal limits. A planned build week above 1.3 is normal training; the value of the number is in flagging increases you did not intend.
Why does this calculator show two different ratios?
The coupled ratio divides this week by an average that includes this week, which is the original formula and what most calculators use. Because the acute week sits on both sides of the division, it creates a statistical artefact known as mathematical coupling. The uncoupled ratio excludes the current week from the chronic average and avoids that problem, so it is the figure shown first here.
Which load unit should I use?
Session RPE — your rating of perceived exertion from 1 to 10 multiplied by the session duration in minutes — is the most practical for runners because it needs no equipment and captures intensity as well as volume. Kilometres, minutes or TSS also work. The ratio is unitless, so the only requirement is using the same unit for all four weeks.
Is ACWR actually proven to prevent injuries?
No. It is associated with injury risk in a number of cohort studies, and the IOC consensus still lists it among load-monitoring tools, but it has not been shown to prevent injuries when used as an intervention. Several researchers have argued the metric is conceptually flawed and should be retired. Use it as one input among sleep, soreness and training history rather than as a decision rule.
My ratio is high but I feel fine. Should I cut back?
Not automatically. A high ratio after a deliberate build week, when you are sleeping well and recovering between sessions, is what progressive overload looks like. The reading is more useful when it surprises you — when you had not realised how much the week had grown, or when it coincides with poor sleep, lingering soreness or a niggle.
Data sources & references
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