Compound Interest Calculator

How do you calculate compound interest with regular deposits?

Enter your starting balance, deposit amount, annual rate and term, then read the automatically updated final balance. For a worked example, use Initial amount of $10,000, Contribution of $200, Monthly for both frequencies, End of each period, a 7% annual rate and 10 years. Leave withdrawals, annual increases, tax and inflation at zero. The final balance is $54,713.58: $34,000.00 contributed, including the initial amount, plus $20,713.58 interest.

The schedule separates money you supply from growth. It does not describe the entire final balance as earnings. These selected rows come from the same calculation; the interactive schedule includes every year between them.

Monthly deposits of $200 on a $10,000 starting balance at 7% compounded monthly

Elapsed time	Contributions to date	Interest to date	Balance
1 year	$12,400.00	$801.42	$13,201.42
5 years	$22,000.00	$6,494.83	$28,494.83
10 years	$34,000.00	$20,713.58	$54,713.58

What is the compound interest formula?

Compound interest adds earned interest to the balance so it can earn further interest. The standard compound interest formula for a lump sum is A = P(1 + r/n)^(nt). P is the initial amount, r is the nominal annual rate as a decimal, n is the number of compounding periods per year, and t is the term in years. With $10,000, 5% compounded monthly and no deposits for 10 years, this gives $16,470.09.

Regular deposits require an additional annuity calculation. When deposits and compounding are both monthly, the end-of-month deposit component is C × ((1 + i)^m − 1) / i, where C is the monthly deposit, i = r/12 and m is the number of months. At zero interest, that component is simply C × m. The tool implements growth period by period, allowing deposit and compounding frequencies to differ without assuming every cash flow happens monthly.

How does compounding frequency change the result?

There are six compounding choices: Daily, Weekly, Monthly, Quarterly, Semiannually and Annually. They use 365, 52, 12, 4, 2 and 1 compounding periods per year respectively. At a positive nominal rate, more frequent compounding raises the effective annual rate. For 5% nominal, annual compounding gives 5.000%, quarterly about 5.095%, monthly about 5.116% and daily about 5.127%.

Contribution frequency is independent: Weekly means 52 contributions per year and Every 2 weeks means 26. Neither uses actual calendar dates. To compare deposit schedules fairly, adjust the contribution amount as well as its frequency; keeping $200 while switching from monthly to weekly increases the annual amount you put in. The calculator does not automatically preserve an annual savings budget when changing this selection.

Does contribution timing matter for partial periods?

Yes. Start of each period applies the cash flow before growth, while End of each period applies it afterward. Starting with zero and depositing $100 monthly at 6% compounded monthly for 10 years gives $16,387.93 with end timing and $16,469.87 with start timing. The $12,000 deposited is identical; the difference comes from how long each deposit earns interest.

A final partial period grows at an equivalent rate for its fraction of a year. With end timing, no cash flow is added unless its scheduled boundary falls within the term. With start timing, the opening cash flow still occurs even if the term ends before the first full period. For example, with $1 initially, a $100 yearly contribution, zero interest and a six-month term, start timing gives $101; end timing leaves $1. This matters when comparing yearly contributions over a short term.

How do annual contribution increases work?

Annual contribution increase (optional) raises the deposit amount after each complete year of contribution periods. It changes deposits, not the interest rate. For $100 monthly and a 3% increase, deposits are $100 in the first year, $103 in the second and $106.09 in the third. Starting at zero with zero interest, those three years contribute $3,709.08 altogether.

The increase is a fixed assumption you enter, with an accepted range of 0% to 100%. It is not automatically linked to the inflation field. You can enter the same percentage in both fields to explore that assumption, but the tool does not track actual price changes or changing income. Goal mode instead uses level contributions and does not apply annual increases.

Can you solve for a target savings balance?

Enable Solve for a savings goal and enter Target balance (before tax). The result adds Required contribution per period (before tax), using the selected frequency, timing, rate and term. Starting with $10,000 and targeting $100,000 over 10 years at 7% compounded monthly requires an end-of-month contribution displayed as $461.64. The calculation retains more precision internally, so re-entering the rounded amount can produce a slightly different final balance.

The target is nominal and before tax. Tax and inflation adjustments remain separate results rather than constraints on the solver. A target already covered by projected principal growth can require zero contributions. If the term contains no payment date and the initial investment cannot reach the target, there is no valid contribution solution. Comparison and annual increases are available in projection mode instead.

What happens when withdrawals exhaust the balance?

Enter a nonnegative amount in Withdrawal per contribution period (optional). At each selected boundary, the calculator adds the deposit first, then withdraws up to the funds available. Withdrawals use the same frequency and start/end timing as contributions. Annual deposit increases do not increase withdrawals.

With $1,000 initially, no deposits, zero interest, $300 monthly withdrawals and a six-month term, the first three withdrawals total $900. The fourth takes the remaining $100, and subsequent unfunded withdrawals take zero. Total withdrawals are $1,000 and First depletion identifies period 4. Depletion records the first withdrawal boundary that leaves zero; it does not halt future scheduled deposits. Total interest accounts for withdrawals as balance minus cumulative contributions plus actual withdrawals, so taking money out is not itself counted as an investment loss.

What are nominal and inflation-adjusted returns?

Final balance is the nominal amount before the optional tax deduction. The calculator taxes only positive accumulated interest once at the end, capped at the remaining balance. Negative total interest produces no tax deduction or tax credit. This simplified model does not deduct tax each year or distinguish account types, allowances, countries or tax brackets.

Inflation-adjusted balance divides the after-tax balance by (1 + inflation/100)^t, using the full term including extra months. Applying 20% tax and 3% inflation to the opening worked example leaves $50,570.86 after tax and $37,629.47 in today's purchasing power. The original $54,713.58 headline remains the pre-tax nominal balance. There is no separate fee calculation; enter your own net-of-fees rate. Use Percentage Calculator for supporting percentage arithmetic.

How do you read, compare and save the results?

The chart normally stacks cumulative contributions and interest with solid and striped fills. For negative interest or withdrawals that make a stacked total misleading, it switches to available balance bars. Year-by-year schedule lists cumulative contributions, interest and balance at each complete year, plus a final partial-year row when needed. Download CSV exports those same rows with monetary values rounded to two decimal places; it is not a transaction-by-transaction statement.

Compare with a second scenario lets you change Scenario B rate (%) and Scenario B contribution. Other assumptions, including annual increases and withdrawals, are shared. The panel reports Scenario A, Scenario B and Difference (B - A) using pre-tax final balances. It does not solve a second goal or display a separate inflation-adjusted comparison.

Calculations run in the page, and the form is encoded in the address fragment after #. Copy that address to restore or share inputs; the recipient sees the financial assumptions contained in the link. Missing or malformed fields fall back individually to defaults, while numeric values outside accepted limits can still require correction. The CSV contains results, whereas the address preserves the scenario settings.

What limits should you check before using a projection?

The combined term must be positive and at most 100 years, with whole Years and Months from 0 to 11. Annual rates must be greater than -100% and no greater than 100%; negative returns are supported. Initial amount and contributions must be nonnegative, and at least one must be positive. Enter 0 for a lump-sum-only contribution rather than leaving a required numeric field empty. Blank optional inflation, tax, increase and withdrawal fields mean zero.

The model assumes a constant annual rate, fixed intervals and the entered cash-flow rules. It does not model irregular dates, market volatility, varying yearly returns or exchange rates. Amounts display as US dollars; there is no currency conversion. The Loan Calculator serves repayment calculations, while the Discount Calculator handles price reductions. These projections show the consequences of your assumptions, not guaranteed investment outcomes.