My wife and I each have a car, and we both want to track how much we spend of gas each year, per car. We both put gas in each other’s cars, so tracking the per car expenses can be very difficult. I could make a mark on each receipt or I could put receipt in a special place for each car, or I could just track it simply at the pump; with the price.
We simply make sure that all gas purchases for my car end in a “1” (ie. $28.41) and all purchases for her car end in an “2”. Any time I buy gas for someone else or for yard equipment, I end it in a “3”. Then when we reconcile our credit card statements in Quicken, I know exactly how to categorize the purchase.
An added bonus with this system is that any gas purchase made with my credit card with a number other than 1, 2, or 3 signals a red flag and requires investigation.