What Compound Interest Actually Is
Compound interest is interest that earns interest. In the first period your money grows by the rate; in the second period the larger balance grows by the same rate; and so on, each period starting from everything that came before. The gap between that and simple interest — where only the original amount earns the rate — starts trivial and ends enormous. On a lump sum at the illustrative 2.00% example rate the difference over ten years is small; at higher rates and longer horizons it becomes the single most powerful force in personal finance.
The mathematics is a geometric progression: with annual compounding, a principal P at rate r for t years becomes P × (1 + r)t. Compounding m times a year replaces the exponent accordingly, which is why the frequency selector changes the result even at an identical annual rate. For frequencies other than monthly, the calculator converts the selected annual compounding frequency into an equivalent monthly rate to run the month-by-month model — an approximation, not a literal re-creation of each bank's crediting dates. Contributions slot in as a growing annuity: each month's deposit starts compounding from the moment it lands, and regular contributions are assumed to be added at the end of each month.
Why Frequency Matters
At the same nominal annual rate, more frequent compounding means interest starts earning interest sooner. The calculator quantifies this for your own numbers — the results card shows how much extra monthly compounding earns compared with annual at the rate you entered, and the table makes the gap visible year by year. The effect is real but second-order: it is dwarfed by the rate itself and by time. A 0.5 percentage point better rate or two extra years of patience will do more than switching annual to daily compounding ever will.
The Rule of 72
A handy mental shortcut: divide 72 by your annual rate (in percent) and you get roughly the number of years it takes money to double. At 3%, about 24 years; at 6%, about 12. It is an approximation — the true doubling time at 2% is closer to 35 years than 36 — but it is accurate enough to steer by, and the results card computes it for whatever rate you enter. The rule works the same in every currency, including Chinese yuan.
Using This Calculator for CNY Goals
The rate box deliberately starts at a round 2.00% marked as an illustrative example — not a forecast and not the current market. Replace it with a rate you can actually justify: the rate on a deposit product you hold, or a conservative long-run assumption for an investment portfolio. For fixed-term deposits remember that interest is typically paid simple per term; compounding happens when you roll over, which annual compounding approximates. For anything riskier than deposits, expected returns are uncertain and can be negative — treat the projection as a scenario, not a promise.
Related China Calculators
- China Savings Calculator — the goal-oriented version of this projection.
- China Mortgage Calculator — compounding working for the bank instead of you.
- China Loan Calculator — what borrowing costs at the same maths.
Frequently Asked Questions
What is the difference between nominal and effective rates?
The nominal rate is the headline annual rate; the effective rate is what you actually earn once compounding is taken into account. 2% compounded monthly yields about 2.02% effective over a year — small at low rates, larger at high ones.
What rate should I enter?
A rate you can justify: your deposit account's quoted rate, or a conservative assumption for an investment. The 2.00% in the box is an illustrative example only — NOT a current Chinese market rate. Finance Atlas never pre-fills a market rate or forecast.
Does the calculator include tax on interest?
Ordinary RMB bank deposit interest is currently free of individual income tax in China (suspended since October 2008), so no tax is deducted here. Other products may be taxed differently.
What does compounding frequency change?
How often interest is credited and starts earning its own interest. More frequent compounding yields slightly more at the same nominal rate. The calculator uses an equivalent monthly rate to model the selected annual compounding frequency, with regular contributions assumed to be added at the end of each month — the results card shows the difference between annual and monthly compounding at your entered rate.
Is the projection guaranteed?
No. It is a mathematical scenario at the rate you enter. Deposits pay contractual rates, but investment returns vary year to year and can be negative. Treat the number as a planning aid, not a promise.
Disclaimer: Finance Atlas is not a licensed financial adviser in the People's Republic of China. This calculator provides educational estimates only and does not constitute financial advice or an investment recommendation. Projected returns are not guaranteed.