Interest on a loan under the microscope: the greatest ally in reducing tax!

You pay interest on a loan and treat it as a cost that simply “has to be borne”? That is one of the most common mistakes. In practice, interest can reduce tax in a tangible way – provided it is clear when and how it should be claimed. This article shows which financing costs can be deducted, how much can be saved, and where money is most often lost without noticing. Find out how to turn a loan into a tax optimisation tool.

Loan interest – when does it actually reduce tax?

Loan interest can be deducted when it is directly connected with the generation of income, for example from renting out property. This is the key rule: the loan itself is not decisive, but its purpose. If an apartment is financed for rental purposes, the interest becomes an expense incurred to generate income. The rule is simple: there is a loan for an investment property, it is rented out and generates income, and the interest reduces the tax base, which means lower tax is paid because the “profit on paper” is smaller.

Importantly, the rules even allow a situation in which costs arise before income is earned, for example before rental begins – provided there is a genuine intention to generate income from the property. This is where the advantage of acting with awareness appears: tax optimisation begins even before the first tenant, not only once income starts to be earned.

In practice, loan interest related to a rented property is reported in the German tax return in Anlage V as Werbungskosten, i.e. rental income expenses. As a result, it is not merely a current burden for the borrower, but can materially reduce taxable income. If a property owner pays €4,000 in loan interest during the year and the marginal tax rate is 30%, tax may be reduced by around €1,200. This does not mean, of course, that the tax office “refunds” the full amount of interest, but that including it as an expense reduces the tax base and ultimately allows less tax to be paid on rental income. 

Which loan costs can be claimed as business expenses? Not only interest!

Not only the interest itself can be deducted – the list of financing costs is much broader. Many people focus solely on the amount of the instalments, overlooking other financing costs that can also reduce the tax base. In addition to mortgage interest, costs of establishing security (e.g. a mortgage), notarial fees connected with the loan, and even bank fees and financing arrangement costs may be included as expenses. All this means that the actual cost of the loan for tax purposes may be significantly lower than initially suggested by the instalment amount alone.

A particularly interesting financing element may be the so-called Disagio, i.e. a fee charged upfront in exchange for a lower interest rate. For a loan used to finance a rental property, such a Disagio may be tax-deductible, but not always under the same rules. In practice, a Disagio of up to 5% of the loan amount is usually regarded as market-standard if the loan carries a fixed interest rate or an interest-rate lock-in period of at least 5 years. In such a case, the fee may be recognised as an expense at the outset of the investment. If the Disagio is higher or the loan terms deviate from standard conditions, the Finanzamt may require the excess to be spread over time, for example over the interest-rate lock-in period. 

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If property is financed with a loan, funds from the investment loan should not be mixed with private expenses in one account. Ideally, the documents should show a clear path: loan disbursement → purchase of the apartment, renovation or another expense connected with letting. The Finanzamt looks primarily at where the money actually went. With several loans and one joint account, proving this after a few years can be much more difficult than calculating the interest itself.

Loan before rental – can interest be claimed earlier?

Yes – interest can be claimed even before rental begins, if there is a genuine intention to generate income from the property. This is one of the most underestimated mechanisms and can bring real tax benefits. Imagine the following situation: a plot of land or an apartment is purchased, a loan is taken out and the property starts being prepared for rental – renovation is carried out, formalities are handled, but no income has yet been generated. Even then, the interest may already qualify as a tax-deductible expense, provided there is a clearly defined rental plan and the actions actually lead towards it.

This means that expenses can be reported even before the first rent payment is received, and then claimed once income arises. This approach is used by investors who buy properties “for preparation”, renovate them over several months and only then let them to tenants. Without this knowledge, real money can easily be lost because the full potential of the costs already incurred at the start of the investment is not used.

Early repayment of a loan – when can additional costs be deducted?

The fee for early loan repayment (the so-called prepayment penalty or compensation) can also be a tax-deductible expense – but not always. What happens next with the property is decisive. If the loan is repaid but the property is still rented out, in many cases such a fee may be included in the deductible expenses, which directly reduces tax. The situation changes dramatically, however, when the sale of the property is linked to early repayment – in that case the possibility of deducting this cost is usually lost.

This is particularly important in refinancing or when changing bank offers. At first glance, a lower interest rate may look very favourable, but after taking tax consequences into account, the real saving turns out to be much smaller. For that reason, such decisions should not be based solely on the instalment amount – the total loan cost after tax is what matters, as it shows the true economic advantage of the change.

Sale of property and interest – can it still be claimed?

Yes – in some situations, interest can still be claimed even after the property has been sold. This may seem surprising, but in practice it works and can reduce tax even after the investment has been closed. The condition is simple: if the loan remains outstanding after the sale and it was not possible to repay it in full from the proceeds, the interest may continue to count as a tax-deductible expense.

In addition, if the proceeds from the sale are used for another rental property, tax continuity is preserved, which gives a major advantage to active investors. This is an important strategy for those who trade in property, buy and sell successive units, and build an investment portfolio. Without this knowledge, it is easy to assume that tax treatment ends with the sale – whereas in reality tax can still be optimised and part of the costs recovered.

A loan for private and rental use – how should costs be allocated?

If a property is partly rented out and partly used privately – the interest can be claimed proportionately. This is a very common situation: one floor is rented out, the other is occupied by the owner, or one part of the building is designated for rental. In such a case, only that part of the interest corresponding to the area or section used to generate income is deducted, which directly affects the amount of tax.

The key point here is the correct allocation of costs to the relevant part of the property and the maintenance of clear accounting or separate financial flows. If this is not done, the tax office may impose its own allocation, often less favourable. That is why, in practice, investors increasingly choose solutions that allow clear separation of costs, such as separate accounts or even different loans for individual parts of the investment.

How can a loan be used as a tax optimisation tool?

A loan can materially reduce tax – but only if it is properly planned. The point is not simply to “have a loan”, but to deliberately choose its structure, know which costs can be claimed and when they should be reported. Concretely, this means selecting financing tailored to rental use, analysing costs (for example, the relationship between interest rates and upfront fees) and planning the investment in advance – before the first tenant appears.

Increasingly, investors are turning to solutions such as investment loans structured with tax optimisation in mind, refinancing analysed in terms of actual tax effects, or separating financing for different parts of a property. The effect of such an approach is very concrete: lower tax year after year, better liquidity and greater control over the entire investment, instead of making decisions without adequate preparation.