# How compound interest works (and how often it compounds)

> Learn how often interest compounds on savings and mortgages, why shares and bonds work differently, and how daily, monthly and annual compounding compare.

Canonical HTML: https://getclova.com/blog/how-compound-interest-works

- Author: Clova team
- Published: 2026-07-25
- Reviewed: 2026-09-03

Compound interest means earning interest on your starting balance **and on
earlier interest**. How often that happens depends on the product: an Australian
savings account may calculate interest daily and credit it monthly, while shares
do not have a fixed compounding schedule at all.

The quick answer is that **calculation frequency, payment frequency and
compounding frequency are not always the same thing**. Read the product terms
before comparing rates.

> Try the interactive example in the [compound interest calculator](https://getclova.com/tools/compound-interest-calculator). The values below use its published defaults.

## How often does interest compound?

There is no universal schedule. These are useful starting points, not substitutes
for the terms of a particular account, loan or investment.

| Product               | What commonly happens                                                              | What compounding means                                                                                      |
| --------------------- | ---------------------------------------------------------------------------------- | ----------------------------------------------------------------------------------------------------------- |
| Savings account       | Interest may be calculated daily and credited monthly.                             | Once credited, interest left in the account can earn more interest.                                         |
| Mortgage              | Interest is often calculated daily on the outstanding balance and charged monthly. | Unpaid interest compounds only if the loan terms add it to the balance.                                     |
| Shares or share funds | Prices change and some investments pay dividends or distributions.                 | Returns can compound when gains and income remain invested; there is no daily or monthly interest schedule. |
| Bonds                 | Many bonds pay coupons on set dates and return face value at maturity.             | Returns compound if coupons are reinvested. Yield-to-maturity usually assumes reinvestment.                 |

### Savings accounts: calculated daily, often paid monthly

Many Australian savings accounts calculate each day's interest from that day's
closing balance, add those daily amounts together, then credit the total monthly.
After the credit reaches the account, it becomes part of the balance that can
earn interest in the next period.

“Calculated daily” therefore describes how the bank measures the interest.
“Paid monthly” describes when it reaches the account. The account effectively
compounds monthly if each monthly credit stays in the account, although the exact
method and bonus-rate conditions vary by product.

### Mortgages: daily calculation is not necessarily daily compounding

Major Australian lenders commonly calculate home-loan interest each day on the
outstanding balance and charge the accumulated amount monthly. That does not
automatically mean mortgage interest compounds every day.

With a principal-and-interest loan, scheduled repayments cover the interest and
reduce the principal. If interest is not paid and the contract allows it to be
added to the loan balance, later interest may be charged on that larger balance.
The lender's contract determines when that can happen.

This distinction also explains why an offset balance or an extra repayment can
reduce interest: a lower outstanding balance means a lower daily interest
calculation. The calculator on this page models savings and investment growth,
not mortgage repayments.

### Shares: returns compound, but shares do not pay interest

Shares do not compound daily, monthly or annually in the way a bank account does.
Their prices can rise or fall, and some companies pay dividends. Compounding is
an outcome rather than a payment schedule: gains remain exposed to future gains
or losses, and reinvested dividends buy more shares that may generate future
returns.

This is why a “7% annual return” in a projection is an assumption used to smooth
an uneven path. It is not an interest rate, a promise, or a claim that the market
adds 7% once a year.

### Bonds: coupons compound only when reinvested

A conventional bond pays coupon interest on specified dates and returns its face
value at maturity. The issuer normally does not add each coupon to the bond's
principal. Your total return can compound when you reinvest those coupon payments.

Yield-to-maturity calculations usually assume coupons can be reinvested at the
same yield. Actual results can differ when reinvestment rates change or a bond is
sold before maturity.

## How compound interest works

When money in a savings account, super fund or investment earns a return, that
return is added to the balance. The next return is worked out from the new,
larger balance. Simple interest is different because it is only calculated from
the starting amount.

Using the current settings in the chart:

- After 5 years, the balance with regular contributions is
  **$49,623**,
  compared with
  **$14,026**
  from the starting amount alone.
- After 10 years, those balances are
  **$105,197**
  and
  **$19,672**.

Change the starting amount, contribution or return and these amounts update with
the chart. The curve gets steeper because every new period starts with a larger
balance.

### When does compound interest take off?

There is no magic year or minimum balance. At a steady 5% effective annual
return, $10,000 with no extra contributions would grow to about $16,289 after
10 years, $26,533 after 20 years, $43,219 after 30 years and $70,400 after 40
years. The dollar gain in each decade grows because the return is being applied
to a larger base.

Time, the rate of return, reinvestment and additional contributions all change
when the curve begins to look dramatic. A higher assumed return also brings more
risk when it represents an investment rather than a guaranteed deposit rate.

## Daily vs monthly vs annual compounding

At the **same nominal annual rate**, more frequent compounding produces a higher
effective annual rate because interest is added to the balance sooner. For
$10,000 at a nominal 5% rate over one year:

| Compounding frequency | Balance after one year | Effective return |
| --------------------- | ---------------------: | ---------------: |
| Annual                |             $10,500.00 |           5.000% |
| Monthly               |             $10,511.62 |           5.116% |
| Daily (365 periods)   |             $10,512.67 |           5.127% |

Daily compounding produces only $1.05 more than monthly compounding in this
example. The advertised rate, fees, bonus conditions and access rules can matter
far more than the frequency.

If two products instead quote the **same effective annual rate**, their balance
after one year is the same. This is why you need to know whether a quoted rate is
nominal or effective before comparing it.

## The compound interest formula

With no contributions or fees, the base formula is:

$$
A = P(1 + i)^t
$$

- $$P$$ is the starting balance.
- $$i$$ is the effective annual return as a decimal.
- $$t$$ is the number of years.
- $$A$$ is the ending balance.

For example, $10,000 growing at an effective rate of 5% for 10 years becomes
$16,288.95:

$$
10{,}000(1.05)^{10} = 16{,}288.95
$$

When a nominal annual rate compounds several times per year, use:

$$
A = P\left(1 + \frac{r}{n}\right)^{nt}
$$

Here, $$r$$ is the nominal annual rate and $$n$$ is the number of compounding
periods each year. For monthly compounding, $$n = 12$$.

### Adding regular contributions

If $$C$$ is added at the end of each period, the calculator uses:

$$
A = P(1 + j)^N + C\frac{(1 + j)^N - 1}{j}
$$

Here, $$j$$ is the return for each contribution period and $$N$$ is the total
number of periods. The full calculator shows how this formula changes when you
turn on fees or inflation.

## Is there an average compound interest rate?

There is no single “compound interest rate.” The useful rate depends on what you
are modelling.

- A savings account has an advertised deposit rate, which may be variable and
  may depend on bonus conditions.
- A term deposit fixes a rate and payment schedule for a set term, but rules can
  differ on whether interest is paid out or added to the deposit.
- A mortgage rate is the cost of borrowing, applied to the outstanding balance.
- A share-market return combines price changes and income and can be negative.

Use the current rate for the specific product you are modelling. The Reserve
Bank of Australia's deposit-rate tables can help with market context, but an
individual account's disclosure documents are authoritative. A calculator shows
what would happen **if its assumptions stayed the same**; it does not forecast
future bank rates or investment returns.

## Try the formula yourself

Open the full calculator to see the formula update when you change contribution
frequency or turn on fees and inflation.

[Open the compound interest calculator](https://getclova.com/tools/compound-interest-calculator)

## Common questions

### How often does interest compound?

It depends on the product. Many Australian savings accounts calculate interest daily and credit it monthly. Home loans commonly calculate interest daily and charge it monthly. Shares do not have a fixed compounding frequency, while bond returns compound only when coupon payments are reinvested. Check the product terms rather than assuming a frequency.

### How often does mortgage interest compound?

Many Australian home loans calculate interest daily on the outstanding balance and charge it monthly. Daily calculation is not automatically the same as daily compounding: whether unpaid interest is added to the balance depends on the loan terms. Check your lender's contract and statement.

### Do shares pay compound interest?

No. Shares may rise or fall in price and some pay dividends; they do not pay interest on a fixed daily, monthly or annual schedule. Returns can compound when gains and income remain invested, including when dividends are reinvested.

### Do bonds pay compound interest?

A conventional bond usually pays coupon interest and returns its face value at maturity. The bond itself does not normally add each coupon to its principal. Your overall return can compound if you reinvest the coupons, and yield-to-maturity calculations commonly assume that reinvestment.

### Is daily compounding better than monthly compounding?

At the same nominal annual rate, daily compounding produces a slightly higher effective annual return than monthly compounding. But advertised rates may use different conventions, so compare effective rates, fees and conditions rather than frequency alone.

### When does compound interest take off?

There is no single take-off year or balance. Compound growth accelerates from the beginning because each positive return increases the base for the next one. The effect becomes more visible with more time, a higher return, reinvested earnings and regular contributions.

### What is the compound interest formula?

When using an effective annual return, the formula is A = P(1 + i)^t. For a nominal annual rate compounded at regular intervals, use A = P(1 + r/n)^(nt).

## Sources

- [Compound interest](https://moneysmart.gov.au/saving/compound-interest) — Moneysmart
- [Compound interest calculator](https://moneysmart.gov.au/budgeting/compound-interest-calculator) — Moneysmart
- [Understanding compound interest lesson plan](https://files.moneysmart.gov.au/media/ecehtqc5/understanding-compound-interest-lesson-plan.pdf) — Moneysmart
- [Advertised deposit rates, Table F4](https://www.rba.gov.au/statistics/tables/csv/f4-data.csv) — Reserve Bank of Australia
- [Mortgage offset accounts](https://moneysmart.gov.au/home-loans/mortgage-offset-accounts) — Moneysmart
- [How is interest calculated on my home loan?](https://www.commbank.com.au/support.home-loan.home-loan-interest-calculated.html) — Commonwealth Bank of Australia
- [Compare savings and transaction accounts](https://www.commbank.com.au/personal/accounts/comparison-table.html) — Commonwealth Bank of Australia
- [Investing in shares](https://www.asx.com.au/investors/learn-about-our-investment-solutions/shares) — Australian Securities Exchange
- [The dangers of over-diversification](https://www.asx.com.au/blog/investor-update/2025/too-much-of-a-good-thing--the-dangers-of-over-diversification) — Australian Securities Exchange
- [ASX bond calculator](https://www.asx.com.au/markets/trade-our-cash-market/overview/bonds/asx-bond-calculator) — Australian Securities Exchange
- [Bonds](https://moneysmart.gov.au/investments-paying-interest/bonds) — Moneysmart