Mileage. It's one of the most overlooked and misunderstood tax deductions for a couple of reasons: you may not realize how much money this can save you or you may not have a good system to track your mileage. Fortunately, apps can now do this for you, but as CEO of your own finances, you still need to know what you can and can't deduct.

First, here's what's new this year from the IRS -

In 2017, the standard mileage rate is going down a half a cent per mile to 53.5 cents from 54 cents in 2016. That includes the use of a cars, vans, pickups or panel trucks. This is all based on an annual study on the costs of operating an automobile.

Medical and moving expense rates each dropped to 17 cents per mile for medical or moving purposes, down from 19 cents for 2016. For medical reasons, this includes trips to the pharmacy and doctor visits. For moving, this rate applies to each mile driven for your move, if certain conditions are met.

Don't forget to give back. If you serve in an official capacity with a charity-- let's say you're the finance director at your church-- you can deduct 14 cents per mile driven in service of your charity. That's the same rate as 2016.

Sounds pretty cut and dry, correct? Well, for entrepreneurs and executives, it's a little more complicated than that.

Here's a real example from a vending machine owner who knew that he was driving a lot of miles for his business. He already understood that he could deduct mileage anytime he travels from his home to one of his vending locations.

Remember, the 2016 mileage expense rate set by the IRS was 54 cents per mile so if he drove 5,000 miles for his business, that would equal a $2,700 deduction. Since he doesn't have a regular place of business, like an office, all of his vending mileage is deductible. He can also deduct his trips to purchase supplies and any materials used to repair or improve his machines.

Since he also works in a retail store, he cannot deduct his daily commuting miles to that job.

However, when he leaves work to repair a machine, he should track those miles as well. You also have a choice to make when you put a vehicle in service. You can take the standard mileage deduction or the actual expense method (gas, repairs, depreciation, insurance, etc.) if it is more advantageous. Careful though: if you start with the actual expense method, you can't switch. If, on the other hand, you take the standard mileage deduction in the first year, you can switch to the expense method in the next. This is where it helps to have a tax pro run the numbers.

No matter the method selected, our entrepreneur will need to continue tracking his miles-- because he will need to know the business percentage in order to calculate the actual expenses and depreciation. However, a taxpayer can't use the business standard mileage rate for a vehicle after using any depreciation method under the Modified Accelerated Cost Recovery System (MACRS - our tax depreciation system) or after claiming a Section 179 deduction for that vehicle.

Also, the business standard mileage rate cannot be used for more than four vehicles used simultaneously. When you add it all up, don't forget to claim parking costs and tolls, in addition to the standard mileage rate.

It doesn't end here for our ambitious entrepreneur.

Are you starting to add up the numbers? Plus, if our vending machine owner has job-related educational classes, he can deduct the local transportation costs of going directly from work to school at the rate of the standard rate (54 cents for 2016). Same goes if he incurs mileage expenses while looking for new employment in the same occupation/day job.

As you can see, keeping records of your mileage could save you thousands of dollars.

Whether you use an app or an old-fashioned mileage log, your records should include total miles for the year, mileage for each deductible use (business, charitable, educational, medical or moving). You also need a record of times, dates, locations and include the business purpose for your trips.

Sounds like a lot of work? Not really. You're driving anyway-- why not save big time on your taxes with this often-overlooked deduction.