Monthly vs yearly compounding: how much difference does it make?

The short answer

Compounding means interest is added to the balance, and from then on that interest earns interest. The more often it is added, the sooner the new interest starts earning. At the same stated annual rate, more frequent compounding gives a slightly higher balance.

The formula is Balance = P x (1 + r/n)^(n x t), where P is the starting amount, r is the annual rate as a decimal, n is the number of compounding periods per year and t is the number of years. For the background, read compound interest explained.

$10,000 at 5% for 10 years

Going from yearly to monthly adds $181.14. Going from monthly to daily adds just $16.56 more. Even the theoretical maximum, continuous compounding, is only 56 cents above daily. Each step up in frequency gives less, so there is a ceiling.

Nominal rate, APR and APY

The 5% in the table is a nominal annual rate. The last column shows the effective annual rate, the real growth over one year after compounding. For savings products in the US, this effective figure is usually called APY (annual percentage yield). A bank that quotes 5% compounded monthly earns 5.116% APY.

This is why comparing a nominal rate with an APY is misleading. An account paying 5.10% compounded yearly (5.10% APY) is slightly worse than one paying 5.00% compounded monthly (5.116% APY), even though its headline number is higher. Compare like with like. When you shop for savings, compare the APY. For loans, see APR vs interest rate.

What matters more than frequency

The effect of compounding frequency is small next to other inputs. On the same $10,000 over 10 years, with monthly compounding:

• Rate: 4% grows to $14,908.33, 5% to $16,470.09, 6% to $18,193.97. One percentage point is worth more than $1,500 here, compared with $181 for switching from yearly to monthly.
• Time: at 5% monthly, 20 years gives $27,126.40 and 30 years $44,677.44, against $16,470.09 at 10 years.
• Contributions: regular deposits usually dominate, because they add new principal every month.

For the effect of time on doubling, see the rule of 72.

When frequency matters more: high rates and debt

At low rates the gap is tiny. At 2% for 10 years on $10,000, yearly gives $12,189.94 and monthly $12,211.99, a $22.05 difference. At higher rates it widens:

This matters most for debt. Credit cards often compound daily or monthly, so a stated 24% APR costs more than 24% a year as a simple figure. If a balance is left unpaid, it grows at the effective rate. The article on compound interest on debt explains what that means in practice, and the Credit card payoff calculator shows how fast a balance falls with a given payment. (The amounts above are for a balance with no payments; real cards also have minimum payments and fees.)

Try it with your own numbers

The Compound interest calculator models a starting amount, monthly contributions and a rate you choose. It divides the nominal annual rate by 12 and compounds monthly, and it adds contributions at the end of each month, after that month's interest. It excludes taxes, fees and inflation, so treat the result as a projection. To compare against yearly compounding, use the formula above or convert the rate to an effective yearly figure first.

Remember the calculator is monthly, so if your account compounds daily your actual balance will be slightly higher, by an amount close to the monthly-versus-daily gap in the table.

What to take away

• More frequent compounding always helps savers and hurts borrowers, but by smaller amounts as frequency rises.
• Compare savings by APY and loans by APR, not by the headline nominal rate.
• A one-point rate difference or a few extra years usually beats any change in frequency.
• For debt at high rates, frequency has a visible cost, so paying balances down quickly matters.
• Use the calculators for estimates and check your institution's terms for how it actually compounds.

To turn a savings target into a monthly amount, use the Savings goal calculator or read how much to save each month.

Frequently asked questions

Is monthly compounding better than yearly?

For savings, yes, slightly. At 5% over 10 years on $10,000, monthly compounding ends with $16,470.09 against $16,288.95 for yearly. For loans, more frequent compounding costs more.

What is the difference between APR and APY?

APR is the stated annual rate. APY includes compounding, so it shows the real yearly growth. 5% compounded monthly equals about 5.116% APY.

Does daily compounding make a big difference?

Not at normal rates. On $10,000 at 5% for 10 years, daily compounding adds only $16.56 over monthly.

What matters more than compounding frequency?

The interest rate, the length of time and regular contributions. One extra percentage point or a few more years usually outweighs any change in frequency.