I have always hated tracking my business mileage manually. Back before Smartphones I used to have a mileage sheet that I kept in my vehicle and wrote down all the miles I drove for business. Tax deductions are of course the primary reason but for real estate photographers I think it's important to be carefully tracking your mileage so you know what you are spending on vehicle costs (part of your variable cost of showing up - see this post for an explanation of variable costs). You need to be sure that your shoot pricing is recovering your vehicle costs so you need to know your milage stats.
Smartphone apps that will use the GPS in your Smartphone to automatically track and record your mileage automatically have been available for a long while but I only started using one of theses Apps recently.
Here are some of these apps:
These are just the more popular ones, there are many more. I think real estate photographers that aren't using one of these should take a look at these they can save you a bunch of time and money and give you a detailed insight into what your business miles driven.
What is your favorite mileage tracking App?