Calculate your ratio

Enter one number per day for the last 28 days, oldest first and today last. Use 0 for days you did not throw. Separate values with commas, spaces or new lines. If you paste more than 28 values, the last 28 are used. Nothing you type leaves your browser.

Tip: type one week per line (7 values) so it is easy to check. Week 4 should end with today.

Your rolling and EWMA ratios will appear here.

Educational tool, not medical advice. The ratio is unit-free, so any consistent unit works.

What the acute:chronic workload ratio measures

Acute workload is roughly what you did in the last 7 days. Chronic workload is what you have averaged over the last 28 days, a stand-in for the work your arm has adapted to. Divide acute by chronic and you get the ratio. A value of 1.0 means this week matched your recent base. A value of 1.5 means this week was 50 percent bigger than what you have been preparing for.

Tim Gabbett's 2016 review in the British Journal of Sports Medicine made the idea popular with a simple point: athletes who are accustomed to high training loads tend to get hurt less than athletes training at lower loads, and the bigger problem is excessive, rapid increases. In other words, the goal is a high chronic workload reached gradually. That is exactly what a pitcher building velocity and durability is trying to do.

How to count throwing workload

The ratio is only as good as the numbers you feed it. Pick one unit and keep it for all 28 days.

  • Throws. Count every throw, not just pitches in games: catch play, long toss, drill work, plyo balls, bullpens, live at-bats and game pitches. Pitch counts alone miss most of a pitcher's week.
  • Effort-weighted throws. Multiply throws by an effort rating, for example 40 throws at 60 percent = 24, and 25 throws at 100 percent = 25. This captures the difference between recovery catch play and a max-intent bullpen. It is the better choice if you can be honest and consistent with effort ratings.
  • Sensor workload. If you wear a throwing sensor such as the Driveline Pulse, use its daily workload value. Pulse-style workload estimates stress on the elbow for each throw, which is closer to what the tissue actually experiences.

Pitch AI, for example, weights each logged throw by the session's intent level and session type before it calculates the ratio, so a velocity day counts for more than the same number of recovery throws.

Two ways to calculate it

Rolling average (coupled). Acute = total of the last 7 days. Chronic = total of the last 28 days divided by 4, which gives an average week. Ratio = acute / chronic. This is the original method used in the cricket and rugby research. Because the current week is also part of the 28 days, the two numbers are mathematically linked, so the calculator also shows an uncoupled version that compares this week with the average of the previous three weeks.

Exponentially weighted moving average (EWMA). Williams and colleagues (2017) proposed weighting recent days more heavily, since fitness and fatigue fade gradually rather than dropping off a cliff on day 8 or day 29. Each day: EWMA today = load today x λ + (1 − λ) x EWMA yesterday, with λ = 2 / (N + 1). N is 7 for acute and 28 for chronic, so λ is 0.25 and about 0.069. Ratio = acute EWMA / chronic EWMA. This calculator starts both averages from your average daily load in days 1 to 7, then runs them through all 28 days.

The two methods often agree within about 0.1. When they do not, it is usually because of timing: EWMA reacts to a big session two days ago more than to one six days ago, while the rolling total treats them the same.

What the zones mean

RatioZoneWhat it usually means for a pitcher
Below 0.8Below your baseYou are doing much less than you have prepared for. Fine for a planned deload or rest week. If it is not planned, capacity is fading and the next return to full intensity becomes the risky part.
0.8 to 1.3Steady-build rangeThis week fits what you have prepared for. Gabbett (2016) called this the training sweet spot. Chronic capacity grows here when weekly increases stay modest.
Above 1.3 to under 1.5ElevatedA noticeably bigger week than usual. Hold or trim volume for a few days, keep high-intent work purposeful, and pay attention to soreness and readiness.
1.5 and aboveSpikeThe range Gabbett (2016) called the danger zone, linked with higher injury risk in team-sport data. Bring volume and intensity back toward your chronic level, then build again in smaller steps.

Two cautions from the original research matter here. First, the 0.8 to 1.3 and 1.5 numbers were drawn from cricket, Australian football and rugby league, and Gabbett himself wrote that applying them to other sports should be done with caution. Second, Hulin and colleagues (2016) found that rugby league players with high chronic workloads were more resistant to injury at moderate ratios. The ratio describes the change. Your chronic base describes how much you can handle. Building that base is the point.

What baseball research says

Baseball-specific evidence exists, but it is early and the samples are small.

  • College pitchers. Slowik and colleagues (2021) followed 17 college pitchers through a season and found that a week-to-week ACWR change of 33 percent in either direction was the main predictor of a throwing overuse injury the following week. Pitchers outside that band were 8.3 times more likely to be injured, with a very wide confidence interval (1.8 to 54.1). Both spikes and drops mattered.
  • High school players. Mehta and colleagues (2022) analyzed three seasons of sensor data from 49 varsity players. Contrary to their hypothesis, higher chronic load was associated with more throwing-related injuries, especially in pitchers, and subjective arm health scores were also related to injury. Absolute load still matters, especially for younger arms.
  • College preseason. Tabaracci and colleagues (2025) measured nine college pitchers with forearm sensors and found ACWR above 1.27 in four of six preseason weeks, peaking near 1.50. Their takeaway was that preseason ramps are often too steep and should build more progressively.
  • Return to throwing. Reinold and colleagues (2024) used workload modeling to redesign an interval throwing program. A traditional program spent 18 percent of its days outside a 0.7 to 1.3 range and peaked at 1.61. The redesigned program built chronic workload more gradually and peaked at 1.33.

Taken together: avoid sudden jumps and sudden drops, build your base over months rather than weeks, and do not assume that any single ratio makes a given week safe.

Limitations you should know

ACWR is popular, but it is not settled science. Impellizzeri and colleagues (2020) argued that training-load injury research has serious conceptual and methodological problems, including the use of ratios, arbitrary 7 and 28 day windows, and small samples, and recommended relying on traditional progressive overload and the athlete's response. Lolli and colleagues (2019) showed that when the acute week is included in the chronic average, the two values are mathematically coupled, which can create spurious correlations. A 2021 Frontiers in Physiology editorial summed up the field as controversial and in need of more research.

Practical takeaway: use the ratio to spot big changes in your own week-to-week pattern, not as a precise risk score. Pair it with how your arm feels, sleep, soreness and readiness. If you have pain, stop throwing and see a qualified clinician.

How to use it to build capacity

  • Grow the base, not the spike. Add volume or intensity in small weekly steps so the ratio stays in the steady-build range while the chronic number rises over months.
  • Plan the low weeks. A deload week will push the ratio under 0.8. That is fine when it is planned. Re-enter with a moderate week before going back to full intent.
  • Ramp before events. Showcases, tryouts and the first weeks of the season are where spikes happen. Build up to that intensity in the weeks before, so game week is not a 1.5 week. The throwing program progression guide walks through this.
  • Respect game rules too. Workload ratios do not replace pitch counts and rest days. Use the pitch count calculator for Pitch Smart limits by age.

Frequently asked questions

What is a good acute:chronic workload ratio for a pitcher?

Most practitioners aim for roughly 0.8 to 1.3, the range Gabbett (2016) called the training sweet spot, and treat 1.5 and above as a spike. Those numbers come mostly from team sports such as cricket, rugby league and Australian football, so use them as a guide for pitchers, not a hard line.

Is a low ACWR safe?

A planned low week is fine and often useful. An unplanned run of weeks below about 0.8 means you are doing less than you have prepared for, so your chronic capacity starts to fall. The risk shows up later, when you jump back to game or showcase intensity from a smaller base.

Should I use the rolling average or the EWMA ratio?

Use one method consistently and watch the trend. EWMA gives more weight to recent days, which Williams and colleagues (2017) argued better reflects how fitness and fatigue decay. The rolling average is simpler to check by hand. When the two disagree, the timing of your sessions within the week is usually the reason.

What should I count as throwing workload?

At minimum, count every throw: catch play, long toss, drills, bullpens, live work and game pitches. Effort-weighted throws (throws multiplied by an effort rating) are better because 40 throws at 60 percent and 40 throws at max intent are not the same stress. If you wear a throwing sensor, use its daily workload number. Whatever you choose, keep the same unit for all 28 days.

Does keeping ACWR in range prevent arm injuries?

No ratio can guarantee that. Research links large workload spikes with higher injury rates in several sports, and a small study of college pitchers found the same pattern, but the method has real statistical criticisms. Treat ACWR as one planning tool alongside readiness, soreness, mechanics and common sense. Pain is a reason to stop throwing and see a qualified clinician.

Skip the spreadsheet

Let Pitch AI track your workload ratio for you

Pitch AI calculates a 7-day vs 28-day acute:chronic ratio with exponentially weighted averages from the throws you log, shows it as an Acute:Chronic Ratio trend in the app and in Coach View, and adjusts your throwing plan's volume and intensity to keep you building. Target ranges change with your season phase, and the plan pulls back when the ratio stays above 1.50.

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Sources and further reading

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