Is cheaper fuel worth the detour?

Your usual station charges €1.60 per litre. Another station, 6 km away, charges €1.50. On a 40-litre fill-up, the lower price saves €4. If reaching it adds a 12 km round trip, our worked example leaves €2.66 after the extra fuel cost.

These prices and consumption figures are chosen for the calculation, not taken from current stations.

Count the whole detour

Driving 6 km to the cheaper station and 6 km back adds 12 km if your usual fill-up would add no distance. If the station is on your commute, count only the deviation from your normal route, including getting back onto it.

Compare the complete route through each station and subtract the distances. This captures any turnaround while excluding the journey you would have made anyway.

Subtract the fuel used to get there

Price saving (€) = litres bought (l) × price difference (€/l).

Extra fuel cost (€) = extra distance (km) × consumption (l/100 km) ÷ 100 × assumed fuel value (€/l).

Estimated net saving = price saving − extra fuel cost.

Compare the same fill-up volume and fuel type, using the prices you would pay after discounts. In this example, the extra fuel is valued at €1.60 per litre, as if replacing it at that price on a later purchase. This estimates the economic saving; it may differ from the cash difference at the pump today.

Suppose the car uses 7 l/100 km on the extra journey:

Round only the final amount to cents. Higher consumption on the detour, for example in traffic, reduces the saving. See What does 100 km cost in fuel? for the consumption-to-cost formula.

A smaller fill-up changes the answer

On 10 litres, the €0.10 price difference saves just €1. The same 12 km detour costs €1.344 in fuel, leaving a €0.34 loss.

For 40 litres, the €4 saving covers about 35.7 km of total extra distance: 4 × 100 ÷ (7 × 1.60). Beyond that, the detour loses money on fuel alone under these assumptions.

Allow for time and wear

If you value an extra 15 minutes at €2, the unrounded €2.656 saving falls to about €0.66, before tyre wear and other driving costs. If you add a cost per kilometre, check whether it already includes fuel so you do not subtract fuel twice.

Check when a quoted price was recorded. The Lithuanian Energy Agency’s map (in Lithuanian) excludes loyalty-programme discounts, and stations can change prices.

You can keep one car’s fill-ups manually in MyFuel, with optional photo attachments. Its approximate summaries can help you choose a consumption assumption. For a petrol/LPG car, include the costs of both fuels.