When Is the Best Time to Do Fasted Cardio?
Fasted cardio is based on the idea that training with low glycogen stores pushes your body to rely more on fat for fuel. Enter your wake-up time and training goal, and this calculator suggests the optimal window to stay fasted without overdoing it, plus a recommended intensity and duration.
Working out immediately after waking doesn't give your body enough time to fully wake up, raising injury risk, while waiting too long can make hunger too intense to control your effort. That's why the window from 30 to 90 minutes after waking is generally recommended for fasted cardio — hydrate well and do a light warm-up before you start.
Set your intensity based on your goal. For fat loss, low-to-moderate intensity (around 60-70% of max heart rate) sustained for 30-45 minutes tends to favor a higher percentage of fat being used as fuel. For conditioning or endurance, shorter, harder interval sessions of 20-30 minutes are more efficient. Because fasted high-intensity work can trigger dizziness or low blood sugar in some people, pay attention to how you feel and adjust as needed.
Frequently Asked Questions
Not necessarily. Any workout done 8+ hours after your last meal can offer similar effects. Mornings are simply the easiest time to be naturally fasted without extra planning, which is why they're most commonly recommended.
Lower the intensity or stop right away and have a small amount of something sugary. If you're prone to low blood sugar, exercising after a light meal may suit you better than training fasted.