Estimate your VO2max
VO2max is the best single measure of aerobic fitness. This quick method uses the ratio of your maximum to your resting heart rate.
Method: VO2max = 15.3 x (maximum heart rate / resting heart rate), the Heart Rate Ratio Method (Uth et al., Eur J Appl Physiol, 2004). Link between fitness and mortality: Kodama et al., JAMA, 2009. Not a medical test.