Is a cheaper fuel detour worth it?

Calculate the pump saving

Multiply the price difference by the litres you will buy. If one station is 8c/L cheaper and you plan to fill 50 litres, the pump saving is 50 × $0.08 = $4.00. Use litres you actually expect to buy, not your full tank capacity. A nearly full car gets less benefit from the same price gap.

Subtract the detour fuel

Estimate the extra kilometres needed to leave your route, reach the pump and return to your route. For a 12 km round-trip detour in a car using 8 L/100 km, you burn about 12 ÷ 100 × 8 = 0.96 L. At $1.90/L, that costs about $1.82. The $4.00 pump saving becomes roughly $2.18 net fuel saving.

Formula: net fuel saving = (price difference per litre × litres bought) − (extra kilometres ÷ 100 × L/100 km × detour fuel price). This excludes the value of your time, tolls and other costs. Actual road access can make a detour longer than a straight-line estimate.

When the answer changes

• A larger fill increases the value of each cent per litre saved.
• A longer detour, higher fuel use or higher pump price increases detour cost.
• If the cheap station is already on your route, detour fuel may be negligible.
• A stale price may have changed before you reach the pump, so check its report time.

The ACCC recommends comparing fuel prices with apps and websites, noting that coverage and update times can vary. See its Australian fuel-app guide.

Compare your route

OTW estimates detour-adjusted savings for stations you can reach with your current tank. See its method and limits, use the fuel cost calculator for a trip budget, or start with the fuel trip planner.