Non billable time Metric

My last employer did track non-billable time, with a specific emphasis on training. They wanted our non-billable time to be below 20% of all hours worked. and training to be at 10%.

I would not recommend dividing NBH by billable hours because increases and decreases will not be in a straight line anymore.

Think about it: if you reduce your non-billable hours by 25% (say you go from 8 hours per 40-hour week to 6 hours), that's a 25% decrease of your non-billable time (it goes from 20% to 15%).

If you divide by the billable hours instead, you go from 25% to 17.6%, which is a decrease of 29.6%. In other words, the reduction in percentage is bigger than the reduction in hours.