Real mortgage rate: when inflation actually works in your favor

Why the real rate matters more than the advertised rate

When you see a mortgage offer at 3.6%, you’re looking at a nominal rate. What really shapes your finances over 20–25 years is the real interest rate, i.e. the loan rate adjusted for annual inflation.

In any buy or rent comparison, ignoring the real rate can completely distort the picture. A 3.6% loan in a 4% inflation environment is very different from a 3.6% loan with 1% inflation. The buy-or-rent.net simulator explicitly models two key parameters: taux_pret (loan rate) and inflation_annuelle (annual inflation) to show this gap.

Simple definition of the real interest rate on your loan

In personal finance, a very intuitive approximation is:

Real rate ≈ Nominal rate – Annual inflation

Concrete examples:

• Mortgage at 3.6% and inflation at 4% ⇒ real rate ≈ –0.4%
• Mortgage at 3.6% and inflation at 2% ⇒ real rate ≈ +1.6%
• Mortgage at 3.6% and inflation at 0.5% ⇒ real rate ≈ +3.1%

In the first case, even though you pay interest, the real value of your debt shrinks faster than your repayments, because each future euro is worth less due to inflation. That’s where inflation can genuinely work in your favor.

How inflation erodes the real value of your mortgage

Suppose you borrow €250,000 over 25 years at a taux_pret of 3.6%. Your monthly payment (excluding insurance) is roughly:

• Monthly payment ≈ €1,270
• Total interest over 25 years ≈ €132,000
• Total cost of the loan ≈ €382,000

In nominal euros, those €382,000 look heavy. But if inflation_annuelle runs at 3%, the real value of those payments falls year after year.

Numerical example with 3% inflation

Assume your salary roughly tracks inflation:

• Year 1: net salary €2,500/month, mortgage €1,270 ⇒ 50.8% of income
• Year 10: salary +3%/year ≈ €3,263/month, same €1,270 ⇒ 38.9%
• Year 20: salary ≈ €4,387/month ⇒ 29.0%

Your monthly payment is fixed in euros but takes up a smaller and smaller share of your purchasing power. In real terms, it’s as if your mortgage gets lighter every year.

Real mortgage rate vs rising rents

On the rental side, rents are usually indexed to an inflation-linked index (e.g. IRL in France). Over the long term, rent growth tends to be close to inflation_annuelle. In a buy or rent framework, you’re comparing:

• Owner: fixed mortgage payment (taux_pret) + ownership costs (property tax, maintenance…)
• Tenant: initial rent + annual rent increases (often similar to inflation)

15‑year comparison scenario

Simplified assumptions:

• Property price: €300,000
• Down payment: €50,000 → loan €250,000 at 3.6% over 25 years
• Starting rent: €1,200/month
• Inflation_annuelle: 3%
• Rent increase: 3%/year (roughly in line with inflation)

Owner side:

• Mortgage payment ≈ €1,270
• Property tax + charges ≈ €200/month on average ⇒ total €1,470/month

Tenant side:

• Year 1: rent €1,200
• Year 10: rent ≈ 1,200 × 1.03⁹ ≈ €1,565
• Year 15: rent ≈ 1,200 × 1.03¹⁴ ≈ €1,820

After 15 years, the owner still pays €1,270 in mortgage, while the tenant pays almost €1,820 in rent. A low or negative real mortgage rate, combined with rising rents, can tilt the buy or rent analysis toward ownership. But that’s not guaranteed: you must also factor in how your savings would grow if you keep renting.

Inflation, real rate and investing your savings

The buy-or-rent.net simulator lets you compare your taux_pret with a potential investment rate (taux de placement) if you choose to rent and invest instead of buying. The key idea:

• If your real investment return (investment rate – inflation) is higher than the real rate on your mortgage, renting and investing can be financially superior.
• If your real mortgage rate is very low or negative, taking on debt can be a good hedge against inflation.

Example: investing tenant vs owner

Back to our 3.6% mortgage with 3% inflation_annuelle:

• Real mortgage rate ≈ 0.6%

Now assume you rent and invest your down payment and extra savings at an investment rate of 5%, with the same inflation:

• Real investment return ≈ 2%

Purely financially, 2% > 0.6%: your real wealth grows faster than the real cost of the debt you would have taken by buying. In this situation, a detailed buy or rent simulation can show an advantage for the tenant-investor, even though the nominal mortgage rate looks attractive.

When inflation really works in favor of borrowers

1. Fixed mortgage rate below inflation

This is the textbook case where your real rate turns negative. Example:

• Taux_pret: 3.6%
• Inflation_annuelle: 5%
• ⇒ Real rate ≈ –1.4%

You repay a loan whose real burden melts away. If at the same time your property value roughly tracks inflation, you win on two fronts: your debt shrinks in real terms and the asset is inflation‑protected.

2. Rents rising faster than your mortgage payment

With elevated inflation, annual rent increases can be steep. As a tenant, you face this without building equity. If you buy with a low real rate, your mortgage stays flat while rents climb. Over 20 years, the cumulative difference vs renting can reach tens of thousands of euros.

3. Incomes broadly indexed to inflation

If your sector tends to adjust wages regularly, your capacity to service the mortgage improves over time. Your monthly effort becomes lighter in real terms, which the simulator can display year by year in a long‑term buy or rent comparison.

When inflation isn’t enough to make buying attractive

Inflation is not a magic bullet. In a buy or rent decision, there are several situations where a low real rate is not sufficient.

1. Low or falling inflation

If inflation_annuelle drops back to around 1% while taux_pret stays near 3.6%:

• Real rate ≈ 2.6% ⇒ your debt barely erodes in real terms.

In that environment, buying becomes more expensive in terms of purchasing power, especially if property prices stagnate.

2. Strong investment returns for renters

If you can invest at a high investment rate, for example:

• Investment rate: 6%
• Inflation_annuelle: 3%
• Real investment return: ≈ 3%

…while your real mortgage rate would be 0.6%, the “rent and invest” strategy may come out ahead in the buy-or-rent.net simulator, even though inflation is eroding debt.

3. Short holding period

Over 5–7 years, the inflation effect on your debt is limited, but transaction costs are immediate: notary fees, agency fees, potential early repayment penalties. Even with a favorable real rate, buying can cost more than renting over a short horizon because the inflation benefit hasn’t had time to accumulate.

How to use the real rate in your buy or rent thinking

To use the real rate intelligently:

• Compare: taux_pret, inflation_annuelle, and your expected investment rate.
• Project: your monthly effort in real euros (after inflation) over 10, 15, 20 years.
• Simulate: two full scenarios, “buy” vs “rent”, over the same time frame.

The buy-or-rent.net simulator lets you set a taux_pret (e.g. 3.6%) and an inflation_annuelle (2%, 3%, 4%…) to see how:

• The real cost of your mortgage evolves
• Your future rent trajectory compares
• Your net wealth develops in each scenario

Full buy or rent example with the real rate

Let’s compare two people considering the same home for 20 years.

Common assumptions

• Home value: €300,000
• Current rent: €1,200/month
• Inflation_annuelle: 3%
• Rent increase: 3%/year
• Investment rate (ETF portfolio): 5%/year

Scenario A: buy

• Down payment: €60,000
• Loan: €240,000 at 3.6% over 25 years (taux_pret)
• Mortgage payment: ≈ €1,220 excluding insurance
• Borrower insurance: 0.30% of initial principal ≈ €60/month
• Property tax + running costs: about €200/month

Total initial monthly outlay: ≈ €1,480.

In real terms, with 3% inflation, this monthly effort is equivalent to:

• Year 10: 1,480 / 1.03⁹ ≈ €1,140 in today’s money
• Year 20: 1,480 / 1.03¹⁹ ≈ €820 in today’s money

Your real effort steadily declines.

Scenario B: rent and invest

• Year 1 rent: €1,200
• Year 20 rent: ≈ 1,200 × 1.03¹⁹ ≈ €2,170

You invest your €60,000 down payment plus any monthly difference between what an owner would pay and what you actually pay in rent (if the rent is lower at the start). With a 5% investment rate, your capital can grow substantially, but it must be weighed against:

• The future value of the property (inflation‑ or market‑driven)
• The remaining loan balance if you had bought

Depending on property price trends and your actual investment returns, either scenario can win. The real mortgage rate (3.6% – 3% = 0.6%) is a central but not exclusive factor in this buy or rent comparison.

Limits and caveats of focusing on the real rate

Even though the real rate logic is powerful, you need to keep a few caveats in mind:

• Inflation is uncertain: it can drop or stay low for long periods.
• Wages don’t always track inflation: your career path matters.
• Housing markets can stagnate or fall: high inflation doesn’t guarantee rising home prices.
• Other ownership costs (closing costs, maintenance, property tax) can offset part of the inflation benefit.

That’s why it’s risky to simply assume that “inflation will pay off my mortgage”. It can help, but only under certain conditions.

Conclusion: use the real rate, but don’t obsess over it

The real interest rate on your mortgage is a crucial concept to understand how inflation can, or cannot, work in your favor. In a buy or rent decision, it helps you:

• Compare the cost of your loan to the pace of rent increases
• Put your monthly payments into long‑term perspective
• Benchmark buying against an investment‑led renting strategy

However, the best choice always depends on your personal situation: job security, time horizon, risk tolerance, life plans. This article is for information only and is not personalized financial advice.

To see exactly how taux_pret and inflation_annuelle impact your own numbers, test multiple buy or rent scenarios with realistic assumptions and timelines.

Simulate your situation on buy-or-rent.net