Disclosed are methods, systems, and devices for determining a respiration rate. An example method includes capturing by a wearable device over a non-zero time period a PPG signal and making a first determination that, during the non-zero time period, the wearable device has moved less than a threshold amount. Responsive to the first determination, the method includes (i) determining from the PPG signal each of (1) a respiratory-induced intensity variation (RIIV) signal, (2) a respiratory-induced amplitude variation (RIAV) signal, and (3) a respiratory-induced frequency variation (RIFV) signal； and (ii) making a second determination that, based on the RIIV signal, the RIAV signal, and the RIFV signal, a respiration rate is determinable. Responsive to the second determination, the method includes (i) determining the respiration rate and (ii) providing by the wearable device a notification, with the notification being based at least in part on the determined respiration rate.
