Heart rate zones
Zones 1 to 3 and 4 to 5 tracked all day from your watch or strap, with the harder zones weighted more.
Fitness and strain
Strain that knows what you recovered from.
Every heartbeat above rest counts. Sixteen turns heart rate zones, steps and strength minutes into a daily strain number and sets tomorrow's target from tonight's recovery.
Train to a number, not a feeling.
Day strain is time in each heart rate zone plus what you lifted, so a long walk and a hard hour both count honestly.
Strength counts too
Heart rate under-reads a set of squats. Sixteen adds muscular load from your logged sets so lifting days are not scored as rest days.
Log any activity
Runs, walks and rides with a GPS map, laps and pace. Auto detection credits workouts your watch recorded on its own.
Targets from recovery
Green recovery raises the strain target. Red lowers it. You always know whether to push or hold.
Then it changes the day
Measured is not the same as changed.
Movement earns screen time. Hit your strain target, close a walk or finish a set of press ups and Sixteen unlocks the apps you chose, for the minutes you earned.
How earning screen time worksQuestions people ask
How does Sixteen calculate strain?
From minutes in each heart rate zone, weighted by zone, plus a muscular load term from logged strength work. The scale runs 0 to 21 and is described on the Science page. We do not claim it matches any other brand's strain number.
Do I need to start a workout for strain to count?
No. All day heart rate counts. Starting a workout in Sixteen adds GPS, laps and a clean summary, and workouts recorded on Apple Watch flow in automatically.
Does Sixteen track VO2 max?
Sixteen reads the cardio fitness estimate your Apple Watch writes to Apple Health and shows it alongside your trends. It does not compute its own.
SixteenPay once. Keep your data. Earn your scroll.
Sixteen is $99 once for lifetime access, or $19.99 a month. Connect the wearable you already own. No hardware to buy, no membership that expires.
iPhone (iOS 17 or later). Prices in USD.