Sleep tracking accuracy
Winner: Whoop 5.0In our scoring the Whoop 5 takes accuracy 9/10 and the Charge 6 takes 8/10 — a one-point gap, not a chasm. Both report light, deep, and REM stages; Whoop layers a Recovery Score on top of the same nightly data.
The evidence bases differ in depth. Whoop's spec sheet claims continuous, ECG-quality HRV and continuous SpO2, and its review cites a published polysomnography validation of the strap (Miller et al., *Journal of Sports Sciences*, 2020) plus a JCSM crossover trial (Berryhill et al., 2020). The Charge 6 offers sleep stages and SpO2 but spot-checked rather than continuous HRV, and its review leans on the general consumer sleep-tracker validation literature rather than a device-specific PSG study.
We have not run either device against a sleep lab ourselves, so treat this as a comparison of published evidence and scored specs. Practically: both give you the same nightly narrative of how long you slept and roughly how it was split. Whoop gives you a more defensible physiological signal underneath it.

