Free tool
ACWR Calculator
Calculate your acute-to-chronic workload ratio to catch overtraining and load spikes before injury hits. For each of the last 7 days, enter how long you trained and pick how hard it felt.
This estimates your 4-week baseline (chronic) load, so you don't need to have tracked it before.
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How to use the ACWR calculator
The ACWR calculator tells you whether your training this week has jumped too far ahead of what your body is used to — the single most useful early-warning signal for overuse injury. If you want the deep science behind the number first, the full ACWR guide covers that.
What you need before you start
Almost nothing. Specifically:
- A rough memory of how long you trained each of the last 7 days (in minutes).
- A sense of how hard each session felt — easy, moderate, hard, or very hard.
- A rough idea of what a normal training week looks like for you (days per week, typical session length, usual effort).
You do not need a wearable, a heart-rate strap, or any load numbers you've tracked before. The calculator does the math for you.
Step 1 — Fill in your last 7 days
Each row is one day. Enter the minutes you trained and pick the effort that matches how the session felt. The calculator instantly multiplies them into a training-load number (shown on the right of each row) — this is the standard "session-RPE" method sports scientists use, where load = effort × duration.
- Rest day? Leave it at 0 minutes / Rest. It counts as zero — you don't skip it.
- Two sessions in one day? Add the minutes together and pick the effort of the harder one. It's an estimate, not a lab measurement, so close is fine.
- Which effort? Easy is a conversational recovery pace. Moderate is steady work you could sustain. Hard is a quality session you're glad to finish. Very hard is a near-maximal or race-type effort.
Step 2 — Describe a normal week
This is the part most ACWR calculators get wrong: they demand a "chronic load" figure nobody has tracked. Instead, this one estimates your baseline from three simple questions — how many days a week you usually train, a typical session length, and your usual effort. That's enough to approximate the 4-week rolling average your acute week is compared against.
Step 3 — Read your ratio
The result updates live as you type. The big number is your acute-to-chronic workload ratio (ACWR): this week's average daily load divided by your baseline daily load. It lands in one of three zones:
- 0.8–1.3 — Sweet spot. This week is close to what your body is adapted to. Associated with the lowest injury risk.
- 1.3–1.5 — Caution. You've ramped faster than your base. Manageable, but don't stack another jump on top this week.
- Above 1.5 — Danger zone. A load spike well beyond your base — where injury-risk research shows the sharpest increase. Consider backing off.
- Below 0.8. Not dangerous like a spike, but a sustained low ratio usually means fitness is fading — fine for a taper or deliberate easy week, not as a permanent state.
How to read the result honestly
- One reading is a snapshot. The trend across several weeks matters more than any single number. Check it regularly rather than obsessing over one day.
- It's an estimate. Effort ratings are subjective and the baseline is approximated, so treat the ratio as a rough guide, not a precise measurement.
- It's not medical advice. A "sweet spot" number doesn't guarantee you won't get hurt, and a high one doesn't mean you will. It's one input among many, including how you actually feel, sleep, and recover.
Common questions
What's a good ACWR?
Roughly 0.8 to 1.3. That range is repeatedly associated with the lowest injury risk in training-load research. See the full ACWR science guide for where those thresholds come from and their limits.
I don't know my exact minutes — does it matter?
Not much. ACWR is about relative change, not precision to the minute. Reasonable estimates that you apply consistently week to week will give you a useful trend.
How often should I check it?
Once a week is plenty for most people — for example, every Sunday looking back at the week just finished. What you're watching for is a sharp jump, not daily wobble.
Does this replace what the app does?
No. This calculator is a manual, one-week snapshot. Mass in Motion tracks your load automatically every day using an exponentially weighted average, keeps running and lifting on separate streams, and folds ACWR into a wider daily recovery score that adjusts your training — rather than asking you to fill in a form.