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Compound interest rate calculator

Recover the fixed compound interest rate that connects two balances with no interim cash flows.

Calculator

A model year is 365.25 days; a month is one twelfth of that year.

Nominal compound interest rate
9.5690%
Effective annual rate
10.0000%
Interest surplus
$2,100.00
Initial balance
$10,000.00
Final balance
$12,100.00
Investment years
2.0000

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How this calculator works

The balance ratio determines an annual growth factor. The selected compounding frequency translates that factor into a nominal quoted rate; changing the frequency leaves the effective annual return unchanged. A surplus can be positive or negative provided the final balance stays positive. Deposits and withdrawals would distort this two-balance rate.

Formula

j = m[(F/P)^(1/(mt)) - 1]; effective rate = (F/P)^(1/t) - 1. Under continuous compounding, j = ln(F/P)/t.

Worked example

$10,000 growing to $12,100 over two years implies 10% nominal with annual compounding. With $100 becoming $144 in two years, the annual effective rate is 20%.

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Frequently asked questions

Why does the nominal rate depend on frequency?

More compounding periods need a lower nominal quoted rate to create the same effective annual growth.

Can the surplus be negative?

Yes. A final balance below the initial balance implies a negative compound rate.

What if the final balance is zero?

There is no finite continuously compounded rate for a total loss. This solver requires a positive final balance for consistent frequency comparisons.

Sources

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