I am trying to create a metric which would tell us how good or bad a client is. Right now I am using a simple ratio: $ \frac{\text{number of bills paid on time}}{\text{number of bills}}. $ This give me a percentage and it essentially tell us if a client always pays it bill on time ($0$ = never, $1$ = always). For instance, a client who paid only one bill on time is as good as a client who paid 20 bills on time with this metric.
The problem with this metric is that it doesn’t capture the number of bills the consumer had to pay. Does anybody has an idea on how I could capture these two information (paid on time + number of bills) into one single number?