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Loan Amortization Explained: Formula, Payments & Interest (2025)

Learn how loan amortization works, from the formula to payment breakdowns, plus the direct vs. indirect amortization methods used in Switzerland.

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Table of contents

Introduction
What Is Loan Amortization?
What Is the Loan Amortization Formula?
How Loan Amortization Works in Switzerland
How to Choose the Right Amortization Strategy
FAQs
Conclusion

Introduction

A loan is a simple agreement, but the loan amortization formula is the roadmap that shows how you pay it back over time.

Whether you’re buying a home in Zurich, financing a car, or growing a business, understanding how amortization works helps you plan your monthly budget and control how much interest you pay. In Switzerland, this knowledge matters even more, because the way you amortize a loan can also influence your yearly tax burden.

This blog will guide you through the formula, the payment breakdown, and the Swiss-specific rules so you can manage your loan with confidence.

What Is Loan Amortization?

What is loan amortization

Loan amortization is the simple process of paying off a loan through regular, scheduled payments over a set period. Each payment covers two parts: the interest the bank charges on what you still owe, and the principal, which reduces the actual debt.

For example, if you borrow CHF 10,000 for five years, your monthly payment slowly shifts over time. At first, most of it goes toward interest because the balance is still high. As the balance drops, the interest portion shrinks, and more of your payment goes toward the principal. This continues until the loan is fully paid and the balance reaches zero.

Amortized loans are different from interest-only loans. With amortization, every payment reduces the debt. With interest-only loans, your payments cover only the interest, and the original principal stays the same until the end, when it must be repaid in one large lump sum.

Understanding amortization matters because it gives you predictable payments, helps you build equity in assets like a home, and shows you the real cost of borrowing. For businesses, amortization also plays a key role in accounting by spreading the cost of certain assets over their useful life.

What Is the Loan Amortization Formula?

The loan amortization formula is used to calculate two things: your fixed monthly payment and the split between interest and principal for every period. Together, these calculations shape the full amortization schedule.

The first step is finding the fixed monthly payment MMM for a fixed-rate loan:

M = P × [i(1 + i)ⁿ] / [(1 + i)ⁿ – 1]

Where:

P = loan amount
i = monthly interest rate (annual rate ÷ 12)
n = total number of monthly payments (loan term × 12)

For example, a 3% annual interest rate becomes 0.03÷12=0.00250.03 ÷ 12 = 0.00250.03÷12=0.0025 per month.

Once you know the monthly payment, the next step is calculating how much of that payment reduces the principal:

Principal Payment = M – (OLB × i)

Where:

M = fixed monthly payment
OLB = outstanding loan balance at the start of the month
i = monthly interest rate

As the OLB gets smaller, the interest portion drops, and more of each payment goes toward the principal. This is why amortized loans pay down faster over time.

Banks and accountants rely on this formula when setting loan terms, building amortization tables, and recording interest and principal on financial statements.

How Loan Amortization Works in Switzerland

How loan amortization works in Switzerland

Switzerland treats mortgage amortization differently from many other countries, mainly because of its tax system and the role of Pillar 3a retirement savings.

Lenders usually divide a Swiss mortgage into two parts. The first mortgage covers about 65% of the property’s value. Repaying this portion is often optional; many banks do not require amortization as long as you can cover the interest. The second mortgage covers the amount above that threshold, up to roughly 80% LTV. This part must be amortized and paid off within 15 years or before retirement, whichever comes first.

Swiss borrowers can repay this mandatory portion through direct or indirect amortization.

Direct amortization means your payments go straight to the bank and reduce the principal right away. Over time, your mortgage balance drops, and the interest you owe decreases. The trade-off is that your tax deduction for mortgage interest also shrinks each year, which may increase your taxable income.
Indirect amortization works differently. Instead of paying down the mortgage, you contribute regularly to a pledged Pillar 3a account or insurance product. The mortgage balance stays the same throughout the term, and the accumulated 3a funds are used to repay the debt at the end. This keeps your debt (and therefore your mortgage interest deduction) higher for longer. On top of that, Pillar 3a contributions are tax-deductible, creating a double tax advantage. The final payout is taxed separately at a lower withdrawal rate.

Because of these tax benefits, indirect amortization is often the preferred approach, especially for higher-income households looking to optimize long-term financial planning.

How to Choose the Right Amortization Strategy

Choosing between direct and indirect amortization—or a mix of both—depends on your financial goals, your tax position, and how comfortable you are with investment risk.

Step 1: Align your strategy with your financial goals

If you want to grow your retirement savings, indirect amortization is usually the most efficient path. Your Pillar 3a contributions reduce your taxable income while also building the capital that will later repay your mortgage. For many residents and expats, this creates a strong long-term benefit.

Step 2: Compare risk levels

Indirect amortization often involves investing Pillar 3a funds, which can fluctuate depending on market conditions. If you prefer certainty, direct amortization offers a fixed, predictable reduction of debt. Your comfort with investment risk should guide which option feels right.

Step 3: Balance affordability and tax savings

Borrowers with higher marginal tax rates often gain more from the tax advantages of indirect amortization than from the reduced interest costs of direct amortization. Evaluating your current and future tax bracket is key to finding the most cost-effective option.

Step 4: Understand the long-term tax impact in Switzerland

Switzerland’s system—especially the imputed rental value—generally favors keeping a higher mortgage balance. With indirect amortization, your debt stays constant, allowing you to:

Deduct more mortgage interest each year
Deduct your annual Pillar 3a contributions
Combine debt benefits with retirement tax benefits

This dual advantage is why many high earners choose indirect amortization.

Step 5: Ask a local expert for a personalized plan

Because tax rules vary by canton and the optimal strategy depends on income, property value, and interest rate trends, consulting a fiduciary is a smart move.

A financial expert familiar with Vaud can model both strategies and help you choose the one that delivers the strongest long-term benefit for your wealth and retirement planning. Learn more about our comprehensive services on the Fiduciaire Vaudoise homepage.

Maximize your Swiss tax savings with indirect amortization

Stop guessing about your mortgage strategy. Get a free, personalized analysis comparing direct and indirect amortization, tailored to your tax situation in Vaud.

FAQ

The fastest way to amortize any loan is to make extra principal payments. Since interest is calculated only on the remaining principal balance, any additional payment that goes directly to the principal reduces the base amount for the next interest calculation. This cuts down the overall loan term and saves you a substantial amount of total interest.

Conclusion

Amortization is more than just a payment schedule—it's a critical financial lever, especially in the context of Swiss home ownership. Whether you prioritize rapid debt reduction with Direct Amortization or leverage the significant tax advantages of Indirect Amortization via Pillar 3a, understanding the mechanics ensures you maintain control over your financial future and maximize your long-term wealth.

For more articles on finance and tax strategy, be sure to visit the Fiduciaire Vaudoise blog.