TabSalary calculator guide
When cheaper gas is actually cheaper
A lower pump price does not automatically make a detour worthwhile. The relevant comparison is the discount on the gallons you plan to buy minus the fuel consumed on the extra round trip. This calculator isolates that fuel-only break-even point.
Written by the TabSalary editorial team · Last reviewed July 21, 2026
How the calculation works
Net savings = (local price − cheaper price) × gallons purchased − (round-trip miles ÷ MPG × local price)
- Calculate gross savings from the price difference multiplied by gallons purchased.
- Double the one-way detour distance to get round-trip miles.
- Divide round-trip miles by fuel economy to estimate fuel burned, then price that fuel.
- Subtract detour fuel cost from gross savings; a positive number means the trip saves fuel dollars.
Worked example
A station five miles away is 30 cents cheaper and you need 12 gallons. Gross savings are $3.60. A ten-mile round trip in a 30 MPG vehicle burns about one-third of a gallon. Valued at the $3.50 local price, the detour fuel costs roughly $1.16 after the calculator's rounding, leaving about $2.44 before valuing time or vehicle wear.
What this estimate does not include
- Travel time, depreciation, maintenance, tolls, traffic, idling, and the value of your time are excluded.
- Real-world fuel economy varies with speed, weather, load, route, and driving style.
- If the cheaper station is already on your route, use only the additional distance created by the stop.
Use the result as a planning estimate, not as personalized financial, tax, legal, or investment advice.