Compound Interest & Investment Calculator
Project monthly investments with annual, monthly or continuous compounding, an annual balance table, a contribution chart and inflation-adjusted purchasing power.
About this compound interest & investment calculator
Project monthly investments with annual, monthly or continuous compounding, an annual balance table, a contribution chart and inflation-adjusted purchasing power Computes exact algebraic and numerical metrics directly in your browser using IEEE 754 precision without round-trip latency.
Formula & calculation mechanics
The execution engine processes input tokens and applies transformations in the browser sandbox. Specifically, Deposits occur at each month-end, including the final month, and stay fixed in nominal currency. With r=annual rate/100, the equivalent monthly rate i is (1+r)^(1/12)−1 for annual compounding, r/12 for monthly, or exp(r/12)−1 for continuous. Annual mode assumes fractional-year compound growth between deposit dates; it is not a bank interest-crediting schedule. Continuous compounding still uses discrete monthly deposits. For n=12×years, FV=P(1+i)^n+C((1+i)^n−1)/i; when i=0, FV=P+nC. The effective annual rate is (1+i)^12−1.
Worked numerical calculation
Scenario: Load example
Sample input:
Processing: Deposits occur at each month-end, including the final month, and stay fixed in nominal currency. With annual inflation π, purchasing power today is FV/(1+π)^years. Inflation is an effective annual rate; negative inflation represents deflation. The nominal deposits do not increase with inflation. This is the purchasing power of the future balance, not the present value of the contribution stream.
Illustrative output:
Domain range & precision boundaries
Use one currency throughout. Principal, monthly contribution and nominal annual rate must be nonnegative. Years must be an integer from 1 to 40. Inflation must exceed −100%. All fields are required; use 0 for no contribution or inflation. Use a decimal point; signs, e notation, leading zeros and surrounding whitespace are allowed. No grouping separators. Each field allows up to 64 UTF-16 units. Fixed-rate educational projection using binary64 approximations. No tax, fees, withdrawals, variable returns or guaranteed investment performance are modeled. Extreme inputs, overflow and detected underflow are rejected; tiny effects can disappear through floating-point rounding. The chart uses nominal currency units and is not inflation-adjusted. These are mathematical scenarios, not account statements or investment recommendations. Calculations stay in your browser and work offline after loading. No added calculation library, external service, fee or usage quota.
Calculations in Compound Interest & Investment Calculator use standard IEEE 754 precision or exact rational models. Verify significant accounting or tax figures with authoritative references.
In-browser calculation boundary
Formula calculations and numeric evaluations in Compound Interest & Investment Calculator run synchronously in the browser JavaScript engine with zero server telemetry.
Mathematical formulas & precision standards
Mathematical constants, IEEE 754 floating-point standards, and numerical analysis specifications:
- Time value of money: ordinary annuity and equivalent periodic rates
- IEEE 754-2019 (Standard for Floating-Point Arithmetic)
Compound Interest & Investment Calculator verification · Audit standards
How to use it
- Enter principal, a monthly contribution, a nominal annual rate and 1–40 whole years.
- Choose compounding and an annual inflation assumption.
- Compare principal, interest, purchasing power and every annual row.
Frequently asked questions
Which inputs are supported by Compound Interest & Investment Calculator?+
No grouping separators.
How are monthly deposits and compounding handled?+
Boundary constraints concerning "How are monthly deposits and compounding handled?" prevent invalid parameter state mutations client-side.
How is purchasing power calculated?+
Runtime handling of "How is purchasing power calculated?" executes synchronously in your browser tab without remote delays.
What do the chart and table show?+
Year 0 is the opening principal. Each later row follows the twelfth month-end deposit of that year. Annual interest is the increase in cumulative interest; principal includes all deposits. Amounts show up to 12 significant digits, without rounding each monthly cash flow to cents. Scroll to see all columns.