Compound Interest Calculator

Separate Contributions From Interest

Before fees and tax, the final balance equals the starting balance plus net payments and interest. Deposits add money you supply. Compound interest earns further interest in later periods.

Without payments, the formula is FV = P × (1 + r/m)^(m × t). P is the starting balance, r is the annual nominal rate as a decimal, m is compounding periods per year and t is years.

For regular end-period payments, use FV = P × (1 + j)^n + C × ((1 + j)^n − 1)/j. Here C is each signed payment, n is the payment count and j = (1 + r/m)^(m/f) − 1, where f is payments per year.

Beginning-period payments multiply the payment term by (1 + j). At a zero rate, the result is P + n × C.

For $10,000 at 6% with monthly compounding and $100 deposited at each month’s end, one year produces $11,850. That includes $1,200 in deposits and $650 in interest. Beginning-month deposits produce $11,857.

Choose the Compounding Period

At the same nominal rate, more frequent compounding produces a higher effective annual rate when the rate is positive. With $10,000 at 6% for one year and no payments, annual compounding produces $10,600. Monthly compounding produces $10,617 and daily compounding produces $10,618.

Effective annual interest is (1 + r/m)^m − 1. At 6% nominal, monthly compounding gives about 6.17% effective annual interest. This figure excludes fees. A lender’s comparison rate includes specified costs and uses its own loan assumptions.

ASIC Moneysmart’s compound interest calculator also models a starting deposit and regular savings. This tool uses your entered rate throughout the term and treats each payment interval as an equal fraction of a year.

A systematic investment plan (SIP) is a regular-deposit pattern in this model. Choose when each deposit starts earning interest. An entered total return already includes reinvested dividends, so adding the same dividends as deposits would count them twice.

Daily means 365 equal periods each year. Weekly means 52 seven-day periods, so its dated year covers 364 days. Quarterly periods advance three calendar months. Different payment and compounding frequencies use an equivalent rate for each payment period. Simple interest uses the nominal rate.

Compare Simple and Compound Growth

Simple interest earns interest on principal without adding earned interest to that principal. Compound interest adds earned interest to the amount earning future interest.

With $1,000 at 10% for two years, annual compounding produces $1,210. Simple interest produces $1,200. Both calculations hold the starting balance, nominal rate and term constant, with no payments or costs.

For regular payments, this simple model calculates each period’s interest on the remaining capital. Withdrawals reduce capital first, then any accrued interest. A comparison shows “Funds depleted” if that model cannot fund every withdrawal. “Exceeds calculation limit” means the comparison exceeds $1,000 trillion. The selected model still calculates within that limit.

An assumed return models possible growth. It does not establish a recoverable legal loss. Entitlement, causation and the applicable interest rule need separate assessment using the matter’s evidence.

Read the Growth Schedule

The graph compares gross and net balances. Each dated row shows the opening balance, signed payment, interest and net closing balance. The CSV includes fees and tax separately, with every period and the inputs used. The on-page table shows up to 120 rows.

Withdrawals leave less money earning later interest. A withdrawal that exceeds available funds stops that model and shows its figures as unavailable until you correct it. It never silently reduces your requested withdrawal.

The schedule rounds displayed money to cents after calculation. Adding the rounded rows can differ by a few cents from the total. Taxes and fees reduce returns, while inflation changes purchasing power. Changing investment returns need a separate scenario for each assumed rate.

Enter fees per payment period, tax as a percentage of positive period interest and inflation as an annual assumption. Net balance deducts fees and tax for investments. Real net balance divides that result by (1 + inflation)^years. This simplified tax model applies no allowances, deductions or capital-gains rules.

For a hypothetical retirement investment, enter a $100,000 starting fund, 5% annual growth and $500 withdrawn monthly for ten years. The rate is an assumption. This worksheet applies no superannuation contribution rules or pension settings. Use the superannuation calculator for that separate projection.

An index, shares, ETF, crypto or forex scenario uses the return you enter. The calculator retrieves no live prices and promises no investment outcome.

For an estate investigation, use actual records to identify missing money before modelling growth. The executor fraud guide explains the evidence needed to investigate diverted estate funds.

Amounts keep full precision during calculation. Your entries stay in this tab and clear on reload.

Solve for a Starting Amount or Rate

Choose Starting balance or Required rate under the growth options. The target is the net closing balance after the entered costs and tax. The other inputs stay fixed.

The solver accepts non-negative deposits and a positive whole-year term. It searches starting balances from $0 to $1 billion or nominal annual rates from 0% to 100%. Withdrawals and loans are excluded because their cash flows can produce multiple rate solutions.

A target outside those bounds has no supported solution. Zero cash invested or a 100% interest tax can leave the required rate undetermined. The result includes the forward balance for checking.

For a stated interest amount without payments, the implied effective annual rate is ((P + I)/P)^(1/t) − 1. The nominal rate for m periods is m × ((1 + I/P)^(1/(m × t)) − 1).

In the dated panel, choose Starting principal and enter the claimed interest. The reverse solver keeps your dates, rate intervals and payment allocation. It shows the implied principal and recalculates the full schedule forwards. A zero-rate schedule or an inconsistent claim cannot establish a unique principal.

Model Loan Payments and Unpaid Interest

Choose Loan and enter negative regular or dated payments to reduce the balance. Fees add to the debt after each payment period. Set tax to zero. The result is an entered-assumption debt illustration.

A payment below that period’s interest and fees leaves unpaid growth in the balance. The warning identifies this outcome. For a no-repayment reverse-mortgage illustration, set regular payments to zero and enter the loan’s growth rate and fees.

Loan illustrations use the equivalent-period method described above. Use the mortgage repayment calculator for its dedicated repayment and amortisation model.

Check the Calculation in a Spreadsheet or Handheld Calculator

For the default monthly example, enter =10000*(1+0.06/12)^12+100*((1+0.06/12)^12-1)/(0.06/12) in Excel. It returns $11,850.33 before the headline rounds to $11,850.

Without deposits, enter =10000*(1+0.06/12)^12 for $10,616.78. For beginning-month deposits, multiply only the deposit term by (1+0.06/12). The result is $11,856.50.

On a TI-84 home screen, type 10000*(1+.06/12)^12+100*((1+.06/12)^12-1)/(.06/12), then press ENTER. On a basic scientific calculator, work out 1.005^12 first and retain the stored result when calculating each term. These are manual entry steps. CSV download does not connect to a handheld calculator.

For simple interest in a spreadsheet, use =10000*10%*30/365, then =8000*10%*30/365. The intervals produce $82.19 and $65.75. Add the unrounded cells for $147.95.

When judgment-interest figures disagree, compare the selected court’s official rate periods with your rate-change rows. The Federal Court’s interest-rate table separates pre-judgment and post-judgment periods. Then match simple or compound treatment, boundary-day counting, leap-year denominator, payment dates and allocation.

Compare rounding too. Legal Aid NSW’s worked post-judgment example rounds the daily amount to cents. This calculator retains full precision until the interval display, so those conventions can produce different totals.

For an illustrative reconciliation, $10,000 at 10% for 30 days gives $82.19 using 365 and $81.97 using 366. That first interval locates a denominator disagreement. If the first interval matches but the next does not, compare its opening principal, new rate and payment allocation. Export both schedules and reconcile the first different row before comparing totals.