Compound Interest Calculator: See How Your Money Grows Over Time
March 1, 2026
7 min read
Compound Interest Calculator: See How Your Money Grows Over Time
Starting capital + monthly contribution + return + time. See in 10 seconds what CHF 500/month becomes over 30 years — and why compound interest is what Albert Einstein supposedly called the "eighth wonder of the world".
In 30 seconds — what you need to know
- Compound interest = interest on interest. Your money grows exponentially, not linearly — because your already-earned returns also earn returns.
- Rule of 72: 72 ÷ return (in %) = years until your money doubles. At 7% return: ~10 years. At 0.75% savings account: ~96 years.
- CHF 500/month × 7% × 30 years = CHF 610'000. Of which contributed: CHF 180'000. Interest earned: CHF 430'000 (70% of your final wealth comes from compounding).
- Time beats return. Starting at 25, you need ~CHF 380/month at 7% to reach CHF 1M. Starting at 45, you need ~CHF 1'920/month — five times more.
- Fees are negative compound interest. 2% fees over 30 years cost 30–40% of your final wealth. The biggest avoidable return killer.
Albert Einstein reportedly called compound interest the "eighth wonder of the world." Whether he actually said it is debated — the power of compounding is not. Calculate here how your wealth grows over time.
Compound Interest Calculator
Starting Capital CHF 10,000
Your existing savings that you want to invest. Even CHF 0 is a great start — the monthly savings plan makes the difference. → How much do you have free? Budget Calculator
CHF 0 – CHF 500,000
Monthly Contribution CHF 500
The amount you invest every month via standing order. Just CHF 100/month becomes over CHF 120,000 over 30 years at 7%. The standing order is your most powerful ally. → Why the standing order matters
CHF 0 – CHF 5,000 per month
Annual Return 7%
Historical stock market average (S&P 500): ~10% nominal, ~7% after inflation. Conservative: 5-6%. Savings account: 0.5-1.5%. Bonds: 2-3%. The higher the return, the more important low fees become. → Fee Comparison
Historical stock market average: ~7% p.a. after inflation
Investment Horizon 20 years
The longer you stay invested, the stronger the compound effect. 10 extra years can double your wealth. The best time to start was yesterday — the second best is today.
1 – 50 years
Final Wealth
CHF 270,521
Total Contributed
CHF 130,000
48%
Interest Earned
CHF 140,521
52%
Contributed
Interest Earned
Achieve this result with arvy? An arvy savings plan automatically invests your money in quality companies — from CHF 1/month. The arvy founders invest CHF 100,000+ in the same portfolio. → Set up a savings plan
On this page
What Is Compound Interest?
Compound interest means you earn returns not only on your deposited capital, but also on previously earned returns. Your money works for you — and the earnings work for you too. This exponential growth becomes more powerful the longer you stay invested.
A simple example: if you invest CHF 10,000 at 7% return, after one year you have CHF 10,700. In year two, you earn 7% on CHF 10,700 — that's CHF 749 instead of CHF 700. In year three, it's CHF 801. The difference seems small, but over 20 or 30 years, the effect is enormous.
The Rule of 72: When Does Your Money Double?
The Rule of 72 is one of the most useful rules of thumb in finance — and it works without a calculator. It answers the question: "How long until my money doubles?"
Formula: 72 ÷ annual return (in %) = years until doubling.
| Asset class | Typical return | Doubling time | CHF 10,000 becomes … |
|---|---|---|---|
| Equities (long-term) | 7% | ~10 years | after 30 years CHF 76,000 |
| Equity ETF (conservative) | 5% | ~14 years | after 30 years CHF 43,000 |
| Bonds / mixed portfolio | 3% | ~24 years | after 30 years CHF 24,000 |
| Swiss savings account | 0.75% | ~96 years | after 30 years CHF 12,500 |
The Rule of 72 is an approximation — it is exact for continuous compounding and accurate enough for returns between 4% and 12%. Practically more useful than most gut-feel estimates.
The Three Levers of Compound Interest
Time: The most important factor. The earlier you start, the stronger the effect. 10 extra years of investing can mean the difference between a comfortable and a modest retirement. That's why the best time to start investing is: now.
Consistency: A monthly standing order (dollar-cost averaging) is compound interest's most powerful ally. Even small amounts — CHF 200, 300, or 500 per month — add up to astonishing sums over decades.
Return: The difference between 3% and 7% per year may seem small — but over 30 years, it triples the final wealth. That's why it's important to invest in asset classes with higher return potential, like equities — and keep fees as low as possible.
Savings Plan Table: What Becomes of CHF X/Month Over 30 Years?
At 7% annual return (historical stock market average after inflation), with no starting capital:
| Monthly contribution | Contributed over 30 years | Final wealth | Of which interest |
|---|---|---|---|
| CHF 100 | CHF 36,000 | CHF 122,000 | CHF 86,000 (70%) |
| CHF 250 | CHF 90,000 | CHF 305,000 | CHF 215,000 (70%) |
| CHF 500 | CHF 180,000 | CHF 610,000 | CHF 430,000 (70%) |
| CHF 1,000 | CHF 360,000 | CHF 1,220,000 | CHF 860,000 (70%) |
| CHF 2,000 | CHF 720,000 | CHF 2,440,000 | CHF 1,720,000 (70%) |
Read the last column again: at every contribution level, compound interest makes up about 70% of your final wealth — and only 30% comes from your contributions. Your money works harder than you.
Starting Age: Time Beats Return
The most important variable in compound interest isn't the return — it's time. Three people, all targeting CHF 1 million by age 65, at 7% return:
| Starting age | Horizon | Required monthly | Total contributed | From compounding |
|---|---|---|---|---|
| 25 years | 40 years | CHF 380/month | CHF 182,400 | 82% |
| 35 years | 30 years | CHF 820/month | CHF 295,200 | 71% |
| 45 years | 20 years | CHF 1,920/month | CHF 460,800 | 54% |
| 55 years | 10 years | CHF 5,780/month | CHF 693,600 | 31% |
The cost of waiting
Waiting 10 years (starting at 35 instead of 25) means you need to contribute more than double per month. Waiting 30 years (starting at 55 instead of 25) means contributing 15× more — and compounding still only accounts for 31% instead of 82%. Time is the only lever you can't get back.
📚 arvy Book Club
Psychology of Money — Morgan Housel
Why did Warren Buffett get rich? Not because he's the world's best investor, but because he's been investing for 75 years. 99% of his wealth was created after his 50th birthday. Housel's central insight: the real variable in investing isn't return — it's time.
Why Fees Kill Compound Interest
Fees act as negative compound interest. If you pay 2% per year in fees (as with many Swiss banks), that's not just subtracted from your return — it also reduces the base on which future returns are calculated. Over 30 years, high fees can reduce your final wealth by 30–40%.
| Annual fee | Final wealth after 30 years | Lost to fees |
|---|---|---|
| 0% (theoretical) | CHF 610,000 | CHF 0 |
| 0.9% (arvy) | CHF 512,000 | CHF 98,000 (16%) |
| 1.5% (Robo-advisor) | CHF 457,000 | CHF 153,000 (25%) |
| 2.5% (typical Swiss bank) | CHF 380,000 | CHF 230,000 (38%) |
CHF 500/month over 30 years at 7% gross return. At arvy, all-in fees are 0.84–1.11% per year — including management, transactions, stamp duty, and tax statement. → Fees in detail
Concrete Example Calculations
Example 1 — Career starter: CHF 0 starting capital, CHF 300/month, 7% return, 35 years = CHF 531,715. Contributed: CHF 126,000. Interest: CHF 405,715 (76%). More than three quarters came from compound interest alone.
Example 2 — Savings plan from age 30: CHF 20,000 starting capital, CHF 500/month, 7% return, 25 years = CHF 513,951. Contributed: CHF 170,000. Interest: CHF 343,951 (67%).
Example 3 — Conservative from age 50: CHF 100,000 starting capital, CHF 1,000/month, 5% return, 15 years = CHF 475,631. Contributed: CHF 280,000. Interest: CHF 195,631 (41%).
Frequently Asked Questions About Compound Interest
What is compound interest, explained simply?
You earn interest on your money — and then interest on the interest. CHF 10,000 at 7% becomes CHF 10,700 after one year. In year two, you earn 7% on CHF 10,700, not on 10,000 — so CHF 749. This small difference grows exponentially. After 30 years, CHF 10,000 becomes around CHF 76,000 — without a single additional contribution.
When does my money double? (Rule of 72)
Divide 72 by your annual return in percent. At 7% return, your money doubles in ~10 years. At 5%: ~14 years. At 0.75% savings account: ~96 years. At 9%: ~8 years. The rule is an approximation, most accurate between 4% and 12% returns.
How much does CHF 500 per month become over 30 years?
At 7% annual return, CHF 500/month (= CHF 180,000 contributed over 30 years) becomes around CHF 610,000. Of this, CHF 430,000 (70%) comes from the compound effect — only CHF 180,000 is your contribution. In a savings account at 0.75%, it would only be CHF 202,000.
How much must I save monthly to reach CHF 1 million?
At 7% return: starting at age 25, CHF 380/month is enough (40 years). Starting at 35, you need CHF 820/month (30 years). Starting at 45, CHF 1,920/month (20 years). Starting at 55, you'd need CHF 5,780/month — 15 times more than the 25-year-old. The most important variable isn't return — it's time.
What return is realistic for the calculation?
Historical stock market average (S&P 500, MSCI World): ~10% nominal, ~7% after inflation. Conservative: 5-6%. Mixed portfolio (60/40): 4-5%. Bonds: 2-3%. Swiss savings account: 0.5-1.5%. We recommend 6-7% after inflation for long-term equity savings plans.
What's the difference between simple interest and compound interest?
With simple interest, interest grows the same every year (linearly). With compound interest, it grows more every year (exponentially) because it's calculated on the entire accumulated wealth. CHF 10,000 at 7% over 30 years: simple interest = CHF 31,000, compound interest = CHF 76,000. The CHF 45,000 difference is the magic of compounding.
How can I make the most of compound interest?
Three levers: (1) Start early — time is the most important factor. (2) Contribute regularly via standing order — dollar-cost averaging. (3) Keep fees low — 1% difference in fees costs 20-30% of your final wealth over 30 years. Plus: never sell during a crash — compound interest needs time to work.
Does compound interest also work in a savings account?
Theoretically yes, practically no. With a Swiss savings account at 0.5-1.5% and inflation at 1.5-2%, you lose real purchasing power — the compound effect is negative. CHF 100,000 today only has the purchasing power of around CHF 75,000 after 30 years at 1.5% inflation and 0.75% interest. → Inflation Calculator
How accurate is this calculator?
The calculator uses the exact mathematical formula for monthly compounding with regular contributions. But it doesn't account for taxes, inflation, or fees — your actual net result will typically be 15–30% lower. For your real Swiss situation, combine it with our Fee Comparison and Inflation Calculator.
Did Albert Einstein really say compound interest is the eighth wonder of the world?
Probably not. The quote can't be reliably sourced — it first appears in an advertisement in the 1980s, more than 25 years after Einstein's death. But the point stands regardless of attribution: compound interest is mathematically one of the most powerful phenomena in wealth building. Even without Einstein.
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