Training Load (ACWR) Calculator
Enter your last 4 weeks of training volume and this week's total to see your ACWR and which injury-risk zone it falls into.
4-week baseline
ACWR
Lowest injury risk
This estimate uses a generic formula. Connect your Strava/Whoop/Garmin data for a version personalised to your actual training.
Get early accessWhat ACWR is
Acute:chronic workload ratio (ACWR) compares the training you have done this week, your acute load, against your average weekly training over the last 4 weeks, your chronic load, or recent baseline. It is a way of quantifying how sharply your training volume has changed relative to what your body has recently adapted to, rather than looking at this week's volume in isolation.
How it is calculated
ACWR = this week's training volume divided by your average weekly volume over the last 4 weeks. Research on this ratio and injury risk in runners groups the result into bands: 0.8 to 1.3 is associated with the lowest injury risk. 1.3 to 1.5 is a zone of rising risk. Above 1.5 is associated with meaningfully higher injury risk. Below 0.8 does not mean "safer": it suggests undertraining relative to your recent baseline, not reduced risk.
These thresholds are drawn from a 2025 meta-analysis pooling 22 studies on training load and injury risk, and from Toresdahl et al. 2022, which used Strava data from 735 runners training for the NYC Marathon and found a 6% higher likelihood of injury among those who exceeded a 1.5 ACWR in the weeks before the race, a real but modest effect.
Why runners use it
Most training-related injuries follow a spike in volume the body has not had time to adapt to, more than any single week's absolute total. ACWR gives you a quick check on whether this week's training represents a sharp jump from your recent baseline, so you can ramp volume up deliberately instead of by accident.
It is worth being honest about the limits of this number: these thresholds come from bucketing continuous research data into ranges, and the studies behind them describe the bands as guidelines, not hard cutoffs. This calculator estimates a research-derived ratio, not a guarantee: your actual injury risk also depends on factors it cannot capture, like prior injury history, strength training, sleep, running surface, and footwear.
Sources and limitations: see our methodology.
Worked example
Take a runner whose 4-week average is 40 km and who runs 52 km this week.
52 ÷ 40 gives an ACWR of 1.30, right at the upper edge of the 0.8 to 1.3 lowest-risk band. That is a legitimate volume increase, not a red flag, but it leaves no room for another jump next week without crossing into the 1.3 to 1.5 rising-risk zone, so this would be a reasonable week to hold volume steady rather than push it higher again.
FAQ
What is a good ACWR for running?
An ACWR between 0.8 and 1.3 is associated with the lowest injury risk in the research this calculator is based on. This range means your training this week is close to your recent 4-week average, rather than a sharp spike or drop.
What does an ACWR above 1.5 mean?
An ACWR above 1.5 means this week's training volume is meaningfully higher than your recent 4-week average, which research associates with meaningfully higher injury risk. A 2022 study of 735 runners training for the NYC Marathon found a 6% higher likelihood of injury above this threshold.
Is a low ACWR always safer?
No. An ACWR below 0.8 does not indicate lower injury risk: it indicates undertraining relative to your recent baseline. The lowest-risk zone in the research is 0.8 to 1.3, not the lowest possible ratio.
How is ACWR calculated?
ACWR is this week's training volume divided by your average weekly training volume over the last 4 weeks. You can enter the 4-week average directly, or enter each of the last 4 weekly totals and this calculator will average them for you.
Are ACWR thresholds a guarantee against injury?
No. The 0.8, 1.3, and 1.5 thresholds come from bucketing continuous research data into ranges, and the underlying studies describe them as guidelines, not hard cutoffs. Individual injury risk also depends on factors this calculator does not capture, such as prior injury history, strength training, sleep, surface, and footwear.
Why is ACWR debated among sports scientists?
Because the underlying research has real limitations: the thresholds come from observational studies that show correlation, not proven causation, the ratio treats all training volume as equivalent regardless of intensity or terrain, and some researchers have challenged the statistical methods used to derive the original bands. It's a useful heuristic for spotting sharp volume jumps, not a validated clinical tool.