Whoop Strain is the number on the band that nobody reads correctly. Members chase 20s, feel cheated when a heavy squat day scores a 9, and assume a 14 is exactly twice a 7. None of that is how the score works. This guide explains what Strain measures, how the 0 to 21 logarithmic scale is built, how the daily target is set from your Recovery, and how to use it so that it helps you train rather than nag you.
Disclosure: Fitcoin is our product. We are not affiliated with Whoop, Oura, Google, Fitbit, Garmin, Polar, Amazfit, Xiaomi, Samsung, Ultrahuman, RingConn, Hume Health, Bionny, Apple or any other hardware brand named here. We do not sell trackers and we take no affiliate commission. Where Fitcoin appears, it is as the rewards and insights app that reads the data these devices write to Apple Health or Health Connect. Everything below is a wellness estimate for general fitness, not medical advice.
The short answer
Whoop Strain is a 0 to 21 score of cardiovascular load, built from how long your heart rate sat in each of your personal zones. It is logarithmic, so a 10 is not half of a 20: moving from 18 to 19 takes far more work than moving from 8 to 9. Read it against the Strain target Whoop sets from your morning Recovery, not against other people, and stop treating 21 as a goal. Whoop itself describes 18 to 21 as all-out territory you should not visit often.
What Strain actually measures
Strain is Whoop's answer to one question: how much did today ask of your heart? It is not steps, calories or minutes. The band samples heart rate continuously, splits your day into time spent in five heart-rate zones derived from your estimated maximum, and weights higher zones far more heavily than lower ones. Ten minutes at 90 percent of max adds much more Strain than an hour of ambling at 55 percent.
Two versions exist. Activity Strain scores one workout or one detected session. Day Strain accumulates every minute from midnight to midnight, including the commute, the stairs, the stressful call, and the sessions. Day Strain is the number most members quote and it is the one that pairs with Recovery to close Whoop's coaching loop: Recovery says how much you can absorb, Strain says how much you took on.
Whoop is explicit that Strain is cardiovascular. A heavy deadlift session with long rests can produce a modest Strain despite leaving you wrecked, which is why Whoop added a separate Muscular Load figure through Strength Trainer. If you lift more than you run, read both. The wider vendor-neutral view of how these morning and evening scores fit together is in our recovery scores explained guide.
The 0 to 21 scale, band by band
| Strain range | Whoop label | What it usually looks like |
|---|---|---|
| 0 to 9 | Light | Rest day, desk day, gentle walk or mobility work |
| 10 to 13 | Moderate | A steady run, a normal gym session, an active day on your feet |
| 14 to 17 | High | Hard intervals, a long ride, two sessions, or a very busy physical day |
| 18 to 21 | All out | Race day, a long hard event, or stacking sessions with little rest |
Because the scale is logarithmic, the top is deliberately hard to reach. Whoop designed it so that a well-trained athlete on a brutal day and a beginner on their hardest day both land near the top of their own capacity, rather than the beginner being permanently stuck at 6. The trade-off is that people misread the gaps: a 14 and a 17 are both High, but the 17 probably cost close to twice the physiological work.
How Whoop calculates Strain
Whoop has described the method in its own documentation and in published material, and the mechanics are consistent across Whoop 4.0, 5.0 and MG hardware:
- Personal heart-rate zones. Whoop estimates your maximum heart rate and splits effort into five zones (roughly 50 to 60 percent of max up to 90 to 100 percent). Zones update as the band learns you, so the same run can score slightly differently in month three than in week one.
- Time-weighted accumulation. Every minute adds a contribution weighted by zone. Zone 5 minutes are worth many multiples of Zone 1 minutes.
- Logarithmic compression. The accumulated load is mapped onto 0 to 21 with a curve that flattens near the top. That is why Strain can jump from 6 to 12 with one class, then crawl from 17 to 18 after another hour.
- Day-level rollup. Activity Strains do not simply add up. Two 12-Strain workouts do not produce a 24 (the scale stops at 21) and usually do not produce a 17 either. The day total is computed from all minutes together.
Bevel, the popular Apple Watch alternative, uses almost identical logic on a 0 to 100 percent scale, which is why our Bevel Strain score explainer reads like a sibling of this page. The scales differ; the philosophy does not.
Strain targets: the part people skip
Each morning Whoop turns your Recovery into a suggested Strain window. A green Recovery (67 to 99 percent) gets a higher target, often in the 14 to 17 range. A yellow day is nudged toward the low teens. A red day is told to stay under 10. The Strain Coach view shows the target and fills up as the day progresses, and it recalculates as you train, so a lunchtime run will shrink the evening headroom.
The Strain target is the real product. A 15 on a green day is Whoop working as intended. A 15 on a red day is a warning, and stacking three of them is how members end up asking why their Recovery is always low. The right way to use Strain is to stop when you hit the top of the window, not to chase the highest number your friends posted.
Why your Strain looks wrong
A brutal lift scored a 9
Correct behaviour. Strength work spikes heart rate briefly and then rests. Cardiovascular load is genuinely modest even when muscular damage is high. Log the session through Strength Trainer so Muscular Load captures it, and stop comparing lifting days with running days on the Strain axis.
A stressful day at work scored a 12 with no workout
Also correct. Elevated heart rate from stress, caffeine, heat or a hangover counts. Whoop does not know why your heart is at 95 in a meeting; it only knows it was. This is a feature for people tracking total load and an irritation for people who only want workout scores. Use Activity Strain for the latter.
Strain and my watch disagree
They will. Garmin's Training Load, Apple's Training Load, Polar's Cardio Load and Whoop Strain all use different zone definitions, different max heart-rate estimates and different scales. A Whoop 14 has no fixed equivalent in Garmin's number. Pick one system for decisions and treat the others as colour.
Strain seems easier to hit than it used to be
Two causes. Your zones may have shifted as Whoop re-estimated your max heart rate, or your fitness has improved and the same session now sits in lower zones. The second is good news. The first is worth checking in your profile settings if you know your tested max.
Strain on Whoop 5.0 and MG in 2026
The 2026 tier structure does not change Strain. Whoop One at $199 a year, Peak at $239 and Life at $359 all include Strain, Recovery and Sleep; the higher tiers add Healthspan, Stress Monitor, and on Life the MG hardware with ECG and blood pressure insights. If you only want the Strain and Recovery loop, One is enough, as we argue in Whoop 5.0 vs Whoop MG and Is Whoop worth it.
The 5.0 hardware does improve the inputs slightly: a faster processor and a refined motion sensor mean fewer dropped heart-rate segments during grip-heavy work, and fewer dropped segments means fewer artificially low Strains. It is a marginal gain, not a different score.
How to use Strain without becoming a slave to it
- Check the target once in the morning. Do not refresh the number during a session.
- Aim for the middle of the window most days, the top of it two or three times a week, and above it only for events.
- Treat two consecutive days above target as a signal to schedule an easy day, whatever the calendar says.
- For lifting-heavy weeks, judge the week on Muscular Load and sleep, and let Strain sit lower without guilt.
- If you leave Whoop, the same logic works in Apple Watch recovery apps and in Fitcoin's Energy and Recovery views, which read the same overnight signals from Apple Health or Health Connect.
Frequently asked questions
What is a good Whoop Strain score?
There is no universal good number. Whoop labels 10 to 13 Moderate and 14 to 17 High. A good Strain is one inside the target window Whoop set from your Recovery that morning.
Is Whoop Strain the same as calories?
No. Strain is a logarithmic measure of cardiovascular load from time in heart-rate zones. Calories are a separate estimate. Two workouts can burn similar calories and produce very different Strain.
Why is my Strain low after lifting weights?
Strain measures cardiovascular effort, and strength training keeps heart rate elevated for short bursts with rest between sets. Whoop's Muscular Load, logged through Strength Trainer, is the metric built for lifting.
Can I reach 21 Strain?
In principle yes, but Whoop frames 18 to 21 as all-out effort. Because the scale is logarithmic, the last few points require disproportionate work. Regularly hitting 20 or 21 is a sign of overreaching, not fitness.
Does Strain include the whole day or just workouts?
Both exist. Activity Strain scores a single session. Day Strain accumulates every minute from midnight, including non-exercise stress and movement, and is the number paired with your Recovery target.
Do Whoop One, Peak and Life calculate Strain differently?
No. All three 2026 tiers use the same Strain model on 5.0 or MG hardware. Higher tiers add Healthspan, Stress Monitor and, on Life, ECG and blood pressure features, not a different Strain.
Method: Checked September 26, 2026 against manufacturer product pages, published help documentation and independent reviews. Prices are US list at publication unless noted. Fitcoin has no commercial relationship with the hardware brands named here. Wellness estimates only, not medical advice.
Related reading: Whoop Recovery explained, Whoop Recovery always low, Bevel Strain score, Whoop 5.0 review, Best Whoop alternatives, Is Whoop worth it
About the author: Harris Khan is the co-founder and CTO of Fitcoin, a UK fitness-rewards and health-insights app that reads Apple Health and Health Connect.