Payback period (Amortisationsdauer)

Level 2 · Foundations⚙ Method

German termAmortisationsdauer

Payback period is the time it takes for the money a purchase saves or earns to add up to what the purchase cost. Dividing the upfront cost by the periodic benefit gives a number in months or years — the point at which the outlay has paid for itself. A shorter payback period means the money committed is returned, and starts working for something else, sooner.

Why it matters

Payback period turns a vague "is this worth it?" into a comparable number. It shows up whenever a purchase trades an upfront cost for ongoing savings or income: an energy-efficient appliance, a Wallbox (home EV charger), solar panels, a Bahncard (rail discount card), or a bulk purchase versus paying per use. Two options with the same total cost can have very different payback periods depending on how fast the savings accumulate — and the option with the shorter payback frees up cash sooner for whatever comes next.

Payback period says nothing about what happens after the money is recovered, and it ignores the time value of money — a euro saved next year is worth less than a euro saved today. It is a screening tool, not a full return calculation.

The method

1. Identify the upfront cost — the full amount paid now, in euros.
2. Identify the periodic net benefit — the savings or income the purchase generates each period (monthly or yearly), after subtracting any ongoing costs the purchase itself introduces.
3. Divide cost by periodic benefit: payback period = upfront cost / periodic benefit.
4. For uneven benefits (savings that grow, shrink, or vary by period), add up the benefit period by period until the running total reaches the upfront cost, instead of using one division.

Worked example

A household buys a heat pump conversion for €2,000 above what a standard replacement heater would have cost, and it lowers heating bills by an estimated €400/year. The payback period is:

€2,000 / €400 per year = 5 years

After 5 years, the extra €2,000 spent is fully recovered through lower bills; every year after that, the €400/year is net savings rather than cost recovery.

Comparing two options makes the tool more useful than a single calculation does:

Option	Extra upfront cost	Annual savings	Payback period
Better window insulation	€3,000	€250/year	€3,000 / €250 = 12 years
Attic insulation upgrade	€1,200	€300/year	€1,200 / €300 = 4 years

The attic upgrade returns its cost three times faster. Payback period ranks options by how quickly they recover their cost — it says nothing about how much each one keeps saving after that point, or for how long, which is where total lifetime benefit is actually decided.

Check yourself

A rooftop solar installation costs €7,500 upfront and lowers electricity bills by €625/year. What is the payback period in years?

Window insulation costs €3,000 extra and saves €250/year. Attic insulation costs €1,200 extra and saves €300/year. Which has the shorter payback period?

Window insulation, because its total annual savings target is more ambitiousAttic insulation, because dividing its lower cost by its higher annual savings gives 4 years versus 12 years for windowsThey have the same payback period, since both are home insulation upgradesIt cannot be determined without knowing each upgrade's total useful lifespan

Which of the following are true about payback period? (Select all that apply.)

When the periodic benefit varies from period to period, the cumulative benefit is added up period by period until it reaches the upfront cost, instead of using a single divisionA shorter payback period means the money spent is recovered faster, freeing it up sooner for other usesPayback period accounts for the time value of money by discounting future savings back to today's eurosOnce the payback period is reached, the calculation also tells you how much total benefit will accumulate afterward

A household buys a Wallbox (home EV charger) for €1,800. It reduces charging costs by €30/month compared to public charging. What is the payback period in months?