How to Track Gas Expenses Along with Mileage

Miles tell you how far you drove. They are not a gas receipt. If you want fuel in take-home, you need a dollar amount: what you paid at the pump, or an estimate from distance, MPG, and price.

GigMeter can do that estimate when Auto Gas Mileage Tracking is on. Download on the App Store.

Two ways to put gas on the books

Receipt method. Save the pump total as an expense when you fill up. Accurate for that fill. You still have to remember to enter it.

Estimate method. Cost ≈ miles ÷ MPG × price per gallon (or the km / km per litre version). Good for “this shift burned about $18.” Wrong if your real MPG is nothing like the sticker, or if you idled for an hour.

How GigMeter estimates fuel

In Settings → Vehicle & Gas Mileage you pick a car from the EPA/fueleconomy.gov catalog, or add a custom year, make, model, and MPG. Price per gallon (or litre) is one app-wide field. Saving a vehicle during onboarding turns auto gas tracking on. It stays off if you skip the car.

While a session is running, distance can show an approximate gas dollar figure. That live number is not in net yet. At clock out, GigMeter writes one expense named Gas (Estimated), with a note like 68.0 mi ÷ 32 MPG × $3.85/gal. After that it is a normal expense: edit it, delete it, or leave it. It hits net the same way parking does.

If you change mileage later, the gas row does not silently rewrite. Recalculate estimate shows up when the math would move by a cent or more.

What still has to be manual

Parking, tolls, snacks, a car wash: you add those. If auto gas is off, the expense picker points you at Vehicle & Gas Mileage instead of inventing a default Gas category. You can still add your own Gas category and type a pump total.

Changing the saved price later applies to future estimates, not old sessions.

Miles vs a mileage deduction

GigMeter does not multiply miles by the IRS standard mileage rate. If you claim that deduction at tax time, that is a filing choice, not a toggle in the app. The estimate is optional fuel cost for your net, so you can see whether a zone was worth the drive. See 2026 IRS mileage rates for the tax side.