Estimated Future Value
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$ {{ money(totalPrincipal) }} Principal $ {{ money(totalContributions) }} Contributions $ {{ money(totalInterest) }} Interest
$
% / yr
yrs mos
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%
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YearDeposit ($)Interest ($)Ending ($)
{{ r.year }} {{ money(r.depositCum) }} {{ money(r.interestCum) }} {{ money(r.ending) }}
MonthDeposit ($)Interest ($)Ending ($)
{{ r.period }} {{ money(r.depositCum) }} {{ money(r.interestCum) }} {{ money(r.ending) }}
Categories: Calculator , Finance
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Compound interest describes the exponential growth that occurs when each period’s earned interest is reinvested, so every new cycle generates profit on both the original principal and the accumulated amounts. The effect underpins retirement planning, loan amortisation, and corporate project valuation.

This calculator accepts an opening balance, recurring deposits, investment duration, nominal rate, tax on earnings, inflation expectation, compounding frequency, and deposit timing. A lightweight reactive engine iterates month-by-month, inserts deposits, multiplies by the period factor, deducts tax, applies an inflation deflator, and tracks principal, contributions, and net interest.

Test whether a $15 000 bonus plus $250 monthly contributions at 4.5 % nominal, compounded monthly for six years, can fund a postgraduate degree after taxes and rising tuition. Revisit inputs quarterly—policy shifts or market volatility can derail seemingly reliable projections.

Technical Details:

Future-value analysis uses geometric progression. Each period multiplies the balance by $begin:math:text$\\bigl(1+r/n\\bigr)$end:math:text$, where $begin:math:text$r$end:math:text$ is the nominal annual rate and $begin:math:text$n$end:math:text$ the compounding intervals per year. Optional deposits and an inflation factor adjust the trajectory, producing nominal and real balances for scenario comparisons.

Future value with regular deposits:
FV= P 1+rn nt + PMT × 1+rn nt −1 rn × 1+rn s

$begin:math:text$s = 1$end:math:text$ for deposits at the start of each period; $begin:math:text$s = 0$end:math:text$ for deposits at the end.

OutputMeaning
PrincipalTotal original funds and scheduled deposits.
InterestNet earnings after tax deductions.
Ending BalancePrincipal plus interest at the final period.
Real BalanceInflation-adjusted purchasing power.
ParameterMeaningUnitTypical Range
initialInvestmentStarting capitalcurrency0 – 1 000 000
annualContributionYearly depositcurrency / yr0 – 100 000
monthlyContributionMonthly depositcurrency / mo0 – 10 000
interestRateNominal annual rate%0 – 20
compoundFrequencyIntervals per yearenum1, 2, 4, 12
taxRateTax on interest%0 – 50
inflationRateExpected inflation%0 – 8
investmentYearsWhole yearsinteger0 – 50
investmentMonthsExtra monthsinteger0 – 11

Example: $begin:math:text$P = \\$10\\,000,\\;PMT = \\$200/\\text{mo},\\;r = 6\\%$end:math:text$, monthly compounding for eight years, deposits at period end.

n×t=96 r/n = 0.06/12 = 0.005 FV ≈ \$10\,000 × 1.489 + \$200 × 112.028 = \$33\,305
  • Interest rate remains constant for the entire projection.
  • No account fees, minimum balances, or withdrawal penalties are included.
  • Inflation reduces real balance linearly; interaction with tax is ignored.
  • Market volatility, currency risk, and periodic rate resets are outside scope.
  • Zero interest collapses growth to simple deposit summation.
  • High tax combined with low rates can produce negative real returns.
  • Deposits at period start magnify interest disproportionately for short terms.
  • Extremely long horizons may exceed floating-point precision of the browser.

Methodology aligns with corporate-finance texts by Brigham & Houston and actuarial compound-interest tables published by the Society of Actuaries.

All calculations run entirely in your browser, complying with GDPR data-minimisation principles.

Step-by-Step Guide:

Follow these steps to generate your projection.

  1. Enter the Initial investment.
  2. Select a Compound frequency that matches your account.
  3. Add recurring deposits under Annual or Monthly contribution and choose their timing.
  4. Adjust Interest rate, tax, inflation, and investment length.
  5. Press “Calculate” to view summary chips, a growth table, and an interactive charting layer; export CSV for offline analysis.

FAQ:

Does it support withdrawals?Not yet. The current version models only positive deposits.
Can I change currency?The tool inherits your browser’s locale, displaying numbers with the appropriate symbol.
Is inflation mandatory?Set the inflation field to 0 % to see nominal balances only.
Is my data stored?Nothing leaves your device; all inputs and results vanish once you close the tab.
Why is interest lower than expected?Check that deposits occur at period end and verify whether you enabled tax on interest.

Glossary:

Compounding
Earning interest on prior interest.
Nominal Rate
Annual percentage before compounding.
PMT
Regular deposit each period.
Real Balance
Value after removing inflation.
FV
Projected future value.