What this planner works out
This planner combines two separate questions — how many fuel stops a journey needs, and how many rest breaks — and reports both alongside the fuel required.
They are rarely the same number. Modern cars generally have more range than their drivers, so breaks usually dictate the stops rather than fuel.
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Before you plan stops
- Starting fuel is a percentage of tank capacity. A gauge reading is approximate; the figure matters most when it is low.
- The planner assumes an average of 60 mph for the time calculation, which is optimistic for anything other than clear motorway.
- Range is calculated from the fuel you start with, not a full tank.
- Motorway service fuel is consistently among the most expensive. Filling before joining usually saves several pounds.
A 50 litre tank at 45 mpg gives around 495 miles from full — roughly eight hours of motorway driving. Recommended break intervals would require four stops in that time. On almost any modern car, planning around breaks and treating fuel as something to top up at one of them is the sensible order.
How this calculator works
Two independent counts:
Fuel needed = distance ÷ mpg × 4.546 litres
Range = tank × starting % ÷ 4.546 × mpg
Fuel stops = distance ÷ range, rounded up, less one
Break stops = (distance ÷ 60) ÷ break interval, rounded downSubtracting one from the fuel stop count reflects that arriving with the tank nearly empty is acceptable — you do not need a stop to complete the final leg if the range covers it.
Worked example: 250 miles
Using the default figures — 250 miles at 45 mpg, a 50 litre tank 80% full, breaking every 2 hours:
- Fuel needed: 25.3 litres
- Range available: about 396 miles
- Fuel stops required: 0
- Break stops recommended: 2
No fuel stop needed and two breaks recommended — which is the usual pattern. The practical plan is two breaks, filling up at one of them only if the price is reasonable, and otherwise arriving with a quarter tank and filling at a supermarket near the destination.
Common mistakes
- Planning stops around fuel rather than breaks. Breaks are almost always the binding constraint.
- Using tank capacity as starting fuel. Enter what you actually have.
- Assuming 60 mph on a non-motorway route. The time estimate will be optimistic.
- Filling at motorway services by default. It is consistently the most expensive option.
- Leaving the first break until tiredness appears. By then it is already affecting you.
Frequently asked questions
How long can I park at motorway services?
Typically two hours free, after which charges apply and are enforced by camera. The limit is generous for a normal break and catches people who stop to sleep. Where a longer rest is needed, the charge is worth paying — a penalty notice for overstaying is cheaper than the alternative of driving tired.
Why is motorway fuel so expensive?
Limited competition, high site costs and a captive market. The difference from a supermarket is commonly 10 to 20p a litre, which on a 50 litre fill is £5 to £10. Filling before joining the motorway, or leaving at a junction where a nearby town has cheaper fuel, both avoid it — though the second costs time.
Are there alternatives to motorway services?
Leaving at a junction usually finds cheaper fuel and food within a few miles, at the cost of 10 to 15 minutes. For a fuel-only stop that is often worthwhile; for a break it makes less difference, since the time spent off the motorway counts as the break. Trunk road services and truck stops are frequently better value than motorway sites.
Should I fill up before or during a journey?
Before, where possible — home-area prices are usually lower and you start with maximum range and flexibility. The exception is a journey longer than your range, where a planned mid-route stop at a chosen location beats an unplanned one wherever you happen to be.
Is what I enter stored?
No. Figures are processed in your browser and never transmitted or retained.
Related tools
References
- GOV.UK — motorway services, fuel price transparency data and Highway Code guidance
- MoneyHelper — budgeting for motoring and travel costs
Sources are checked at publication and can change — how I choose and check references.