Your navigation app hands you two options: a shorter route through town, or a longer one on the highway. It defaults to sorting by time, sometimes by distance — but almost never by what either route actually costs you in gas. The shorter path isn't automatically the cheaper one, and the only way to know is to run the numbers for both.
Why "shortest" and "cheapest" aren't the same route
Quick answer Navigation apps typically optimize for time or distance, not fuel cost. A shorter route full of traffic lights and stop-and-go driving can use more gas per mile than a longer highway route where the engine holds a steady, efficient speed — so distance alone doesn't tell you which route is cheaper.
It's an easy assumption to make: fewer miles means less gas, full stop. But fuel cost is a function of distance and MPG together, and MPG is not constant across every road type. A route through downtown with a dozen stop signs forces repeated acceleration from a stop, which is one of the least fuel-efficient things an engine does, while a longer stretch of steady highway driving often lets the same vehicle run closer to its most efficient MPG.
This is exactly the kind of comparison a simple mileage figure can't answer on its own — you need both routes' distance and your realistic MPG for each one, then the same formula applied to both: Cost = (Distance ÷ MPG) × Price per gallon.
Why stop-and-go costs more: Every full stop means the vehicle has to accelerate back up to speed from zero, and acceleration is the most fuel-intensive part of driving. A route with frequent stops effectively "resets" that efficiency cost over and over, which is why in-town mileage often runs well below a car's highway MPG rating even over a short distance.
Comparing two routes side by side
Quick answer Enter each route's distance, your expected MPG for that road type, and the price per gallon, then compare the two totals directly. ToolPico's Fuel Cost Calculator has a dedicated "Route" tab built for exactly this — Route A and Route B, side by side, same price per gallon.
Say a driver is choosing between a 300-mile route mostly on the interstate at an estimated 32 MPG, versus a slightly longer 340-mile route that avoids a stretch of tolled highway but runs through more small towns, estimated at 36 MPG because it's flatter and has less traffic. Same gas price for both, since they're filling up in the same region either way.
Illustrative example: two routes to the same destination, $3.49/gal
| Route | Distance | Est. MPG | Gallons | Total cost |
|---|
| Route A (shorter) | 300 mi | 32 | ~9.4 gal | ~$32.72 |
| Route B (longer) | 340 mi | 36 | ~9.4 gal | ~$32.99 |
In this illustrative case, the extra 40 miles on Route B is nearly offset by its better MPG — the two routes end up costing almost the same in gas, despite one being noticeably longer on paper. That's the kind of result a raw distance comparison would never surface, and it's the whole point of comparing routes on cost rather than mileage alone. The calculator's Route tab runs this exact side-by-side comparison and shows which one wins once both numbers are in.
What the comparison doesn't include
Quick answer A route comparison based on fuel cost alone doesn't include tolls, parking, or wear from extra miles — those need to be added on top of the fuel total separately if they apply to one route and not the other.
Gas cost is only one piece of what a route actually costs. If Route A has a $6 toll and Route B doesn't, that toll needs to be added to Route A's fuel total before the two are truly comparable — a route that wins on gas alone can lose once tolls are factored in. The same goes for parking fees at a destination, or simply the extra wear that comes with driving more miles over the life of a vehicle.
Quick way to adjust: Since the calculator's Route tab totals gas cost only, jot down each route's toll or parking cost separately and add it to that route's fuel total by hand — a route with a small fuel-cost edge can flip once a toll is added on top.
When the longer route is actually worth it
Quick answer A longer route is worth taking for fuel savings when the gap is large enough to matter relative to the extra time and mileage it adds — a dollar or two rarely justifies a longer drive, but a bigger gap on a long trip might.
Not every fuel-cost difference is worth acting on. If two routes land within a dollar of each other, most drivers will reasonably pick whichever one is faster or more pleasant to drive, since the "savings" barely covers a coffee. But on a longer trip, where a meaningful MPG gap compounds over hundreds of miles, the dollar difference can be large enough that it's worth factoring into the decision — especially if the more efficient route isn't meaningfully slower.
Running both routes through the comparison before a long trip takes under a minute and replaces a guess with an actual number, which is really the value of comparing routes on cost rather than assuming the shorter line on the map wins by default.
Frequently asked questions
Does the shortest route always use the least gas?
No. Navigation apps usually optimize for time or distance, not fuel cost, and a shorter route full of stop signs and traffic lights can burn more fuel per mile than a longer highway route where the engine runs at a steady, efficient speed. The only way to know which route is actually cheaper is to compare distance and MPG together for each route, not distance alone.
How do you compare the fuel cost of two different routes?
Enter each route's distance, your expected MPG on that route, and the price per gallon, then apply the same formula to both: Cost = (Distance ÷ MPG) × Price per gallon. Comparing the two totals side by side shows which route is actually cheaper in gas, which is not always the one with the shorter distance. ToolPico's Fuel Cost Calculator has a dedicated "Route" tab that runs this comparison for two routes at once.
Why would a route's MPG differ from another route of similar distance?
Steady highway speeds typically let an engine run near its most efficient RPM range, while a route with frequent stops, hills, or low speed limits forces more acceleration and braking, which burns extra fuel per mile. Two routes of nearly identical distance can therefore have noticeably different real-world MPG depending on how much stop-and-go driving or elevation change each one involves.
Should I factor in toll costs when comparing routes?
Tolls are a separate cost from fuel and aren't included in a fuel-only comparison, so if one route has tolls and the other doesn't, add the toll amount to that route's fuel total yourself before deciding. A route can win on gas cost alone and still end up more expensive overall once tolls are added, so it's worth checking both numbers before picking a route.
Is it worth driving a longer route to save on gas?
It depends on how large the fuel savings are relative to the extra time and any added wear from more miles driven, since a longer route also adds mileage to the vehicle. If the fuel savings are only a dollar or two, most drivers will find the extra time not worth it, but for a longer trip where the MPG gap is substantial, comparing the actual numbers first avoids guessing.
Compare two routes' gas cost in seconds
Enter distance, MPG, and price per gallon for Route A and Route B and see which one actually costs less — free, no sign-up.
Try the free Fuel Cost Calculator →
Related guides
A note on the numbers: The dollar figures in this guide use illustrative example inputs (a 300-mile and a 340-mile route, specific MPG estimates, $3.49/gal, etc.) to show how the comparison works, not predictions of your actual costs. Real distances, fuel prices, and route-specific MPG vary, so always plug in your own current numbers. This article is for general informational purposes and isn't financial advice.