Is It Cheaper to Fill the Tank Completely or Add €20–30 of Fuel at a Time?

At a filling station, you can often see two completely different types of drivers.

The first pulls in, puts the nozzle into the tank and barely looks at the total. They fill the tank completely, pay €70 or €80 and drive away knowing that, at least for a while, they will not have to think about fuel again.

The second driver does things differently. “€20, please.” Or €30. A few days later, another €20. Then €25 more. Psychologically, paying a smaller amount at once feels easier, even if it means visiting the filling station more often.

And that is where the old argument begins.

“Filling the tank completely is cheaper.”

“No, a full tank makes the car heavier, so it uses more fuel.”

“It is better to add a little at a time because then you spend less money.”

In reality, all three statements can be either sensible or misleading — depending on what we actually mean by “cheaper”.

A full tank does not automatically give you a discount. But five small refuelling stops are not the same as one larger one if each visit requires a separate trip to the filling station.

Start with the most important point: you pay the same price per litre

Suppose fuel costs €1.60/litre.

If you add 10 litres:

10 × 1.60 = €16.

If you add 50 litres:

50 × 1.60 = €80.

The price per litre is exactly the same in both cases.

That sounds obvious, but this is where one of the most common psychological traps appears. A driver who adds €20 of fuel feels a much smaller hit to the wallet than someone who pays €80 in one transaction.

But if the first driver pays €20 four times during the month, both drivers have ultimately spent the same €80 — assuming they bought the same amount of fuel at the same price.

What does “put €20 in” actually mean?

The amount of money alone tells us very little until we know the price of fuel.

Using our example price of €1.60/l:

Now the practical difference becomes clearer. A driver who adds only 12–13 litres will return to the filling station much sooner than someone who puts in 40 or 50 litres.

Scenario: both drivers use 80 litres per month

Imagine two drivers — John and Martin.

John buys fuel in larger amounts. When the tank drops to a lower level, he adds around 40 litres.

Martin does not like seeing a large number on the receipt. He adds €20 each time, which at our example price means 12.5 litres.

Both use 80 litres during the month.

If both drivers use the same filling station, pay the same price per litre and the station is directly on their normal route, the difference in fuel-purchase cost effectively disappears.

But John has to deal with refuelling twice a month. Martin does it six or seven times.

And this is where costs begin to appear that never show up on the fuel receipt.

Small refills can cost more if you make a special trip to the filling station

If the filling station is directly on your daily route, the extra cost can be almost zero. You pull in on the way, refuel and continue your journey.

But the situation changes if every small refill requires a special detour.

Suppose driving to your preferred filling station and back adds 4 kilometres to the journey.

Your car uses 7 l/100 km.

At our example price of €1.60/l, that is around €0.45.

Once — almost nothing.

But if you make five such dedicated trips in a month:

5 × 4 km = 20 unnecessary kilometres.

And then there is the time spent driving in, waiting, paying and returning to your normal route.

A full tank is heavier. Does that make the car use much more fuel?

Technically, more fuel does mean more weight. A car with a full tank is heavier than the same car with an almost empty tank.

But that does not mean a full tank suddenly makes the vehicle dramatically less efficient.

Many other factors affect consumption at the same time: driving speed, acceleration, tyre pressure, temperature, traffic, air conditioning, route and luggage.

If you want a more detailed look at the effect of weight, read our separate article about how much extra weight in a car affects fuel consumption — including a full tank, luggage and passengers.

But what if fuel becomes cheaper tomorrow?

This is another common argument: “Why fill the tank today? Maybe the price will fall in three days.”

Yes, it might.

But the opposite can happen too.

Trying to catch the perfect cheapest day can therefore quickly turn into guesswork.

Still, it helps to understand the size of the potential saving.

Suppose fuel costs €1.55/l today, but later rises to €1.65/l.

The difference is €0.10/l.

That helps put the decision into perspective. Is it worth driving across half the city, waiting in a queue and changing your day's plans to get that particular price?

Sometimes yes. At other times, the extra time and kilometres consume a large part of the saving.

When can filling the tank be a smart move?

Not because “a full tank is always cheaper”, but because a larger refill makes a lot of sense in certain situations.

1. Before a long journey

If you have several hundred kilometres ahead of you, a fuller tank means one less thing to worry about. You do not have to search for a filling station in an unfamiliar place or change your route because the estimated remaining range is getting close to zero.

2. If filling stations are not on your daily route

The less often you need to make a dedicated refuelling trip, the fewer unnecessary kilometres and minutes you spend.

3. If you drive a lot

For a driver covering several hundred kilometres each week, adding only 10 or 15 litres at a time can become annoyingly frequent.

4. If you find a good price on your route

If the station is already on your route and the price is clearly attractive, buying a larger amount allows you to use that price for more fuel.

5. If you do not want to keep thinking about the fuel level

Convenience also has value. Not every calculation needs to end in cents. If a fuller tank means you do not have to think about refuelling for the next two weeks, that is a perfectly reasonable advantage for many drivers.

When is adding only €20–30 completely reasonable?

Small refills should not automatically be treated as a bad habit. For some people, they make perfect sense.

1. When cash flow matters right now

Not everyone has €70 or €100 that they can comfortably leave at a filling station in a single transaction.

If the budget is tight before payday, adding €20 or €30 may be much more sensible than filling the tank and leaving the bank account almost empty.

Here, mathematics is not the only consideration. Everyday financial flexibility matters too.

2. If you drive very little

If you cover only 200 or 300 kilometres per month, there is no practical need to buy a large amount of fuel every time purely on principle.

3. If the filling station is literally on the way

If you pass several filling stations every day, the inconvenience of smaller refills becomes much less important.

4. If you want strict control over a weekly budget

For some people, a fixed fuel allowance — for example €30 per week — helps make unnecessary journeys more visible and keeps overall spending under control.

It does not make the fuel cheaper per litre. But it may change the driver's own behaviour.

The psychological trap: “I only spent €20 on fuel”

Small refills create an interesting effect — the expense becomes less noticeable.

€20 on Monday.

€25 on Friday.

Another €20 the following Wednesday.

Then €30 at the weekend.

None of those amounts looks dramatic on its own. Together, however, they already total €95.

A full tank can create the opposite psychological effect

Interestingly, a full tank has its own trap as well.

When the fuel gauge is sitting on “FULL”, some drivers start to feel as though driving does not cost anything.

The fuel has already been paid for, after all.

One more trip to the shop feels harmless. A quick drive for coffee feels free. Maybe a Sunday drive for no particular reason.

Of course, the fuel has not become free. You simply paid for it earlier.

The fuel gauge shows litres in the tank, not free kilometres.

Is it better to drive until the tank is almost empty?

There is no need to go to the opposite extreme either.

Some drivers deliberately wait until the low-fuel warning light comes on before they even start thinking about refuelling. If the daily route is familiar and filling stations are everywhere, this may seem harmless.

But real life does not always follow the plan.

• an unexpected journey appears;
• traffic builds up on the motorway;
• your usual filling station is closed or no longer convenient;
• you suddenly need to pick up a child;
• the route changes;
• in winter, you may not want to search for fuel late at night.

Fuel reserve is not only an economic issue. It is also a reserve of convenience and flexibility.

Which option wins when we count time?

We count money very carefully. We are usually much less careful about counting our time.

Suppose one filling-station stop — entering, taking the nozzle, refuelling, paying and leaving — takes only six minutes.

Of course, these are only examples. If the station is empty and directly on your route, the stop may be quicker. If there is a queue or you have to make a special trip, it can take much longer.

But the point remains: more frequent refuelling costs not only fuel, but also time.

Which option suits you best?

The smarter compromise: not “full tank or €20”, but a chosen fuel level

For many drivers, a third option works best.

You do not have to wait until the tank is almost empty.

You also do not have to fill it to the maximum every single time.

Instead, create a simple system for yourself:

This avoids both extremes — constantly driving with an almost empty tank and filling “right to the top” simply because that is what you have always done.

Mini test: what type of refuelling driver are you?

7-day experiment: count filling-station visits as well as euros

If you normally buy fuel in small amounts, do not deliberately change anything for one week. Simply observe your normal behaviour.

Then ask yourself a simple question: if next week I refuelled once or twice but added a larger amount, would my overall routine become cheaper — or simply more convenient?

For some drivers, the answer will be yes. For others, almost nothing will change. That is exactly why there is no single rule that works for everyone.

Myths and facts

Frequently asked questions

Conclusion: which option actually wins?

If we look only at the price of the fuel itself, the answer is simple: when the price per litre is the same, there is no financial magic in either a full tank or a €20 refill.

If you use 80 litres in a month, sooner or later you will have to pay for 80 litres.

But everyday life adds three more factors.

First — time. The smaller each refill, the more often you have to stop at a filling station.

Second — extra kilometres. If the filling station is not directly on your route, frequent small refills can create unnecessary journeys.

Third — your personal budget. Not everyone benefits from paying a large amount in one transaction, even if the long-term total is exactly the same.

For most drivers, the most sensible solution is therefore not an extreme.

You do not need to fill the tank completely every single time. But repeatedly visiting a filling station for only 10–15 litres simply because you do not want to see a larger number on the receipt does not make much economic sense either.

A better strategy is to add enough fuel to avoid unnecessarily frequent filling-station visits, refuel when a suitable station is already on your route and judge your spending over an entire month rather than by one receipt.

Driver's short takeaway: neither a full tank nor a €20 refill makes fuel cheaper by itself. The best option is the one that reduces unnecessary trips to the filling station, lets you take advantage of a sensible price and still fits comfortably into your monthly budget.