| Year | Deposit (yr) | Interest (yr) | Deposit (cum) | Interest (cum) | Ending ($) |
|---|---|---|---|---|---|
| {{ r.year }} | {{ format(r.depositYr) }} | {{ format(r.interestYr) }} | {{ format(r.depositCum) }} | {{ format(r.interestCum) }} | {{ format(r.ending) }} |
Compound interest turns steady saving into exponential growth by adding earned returns to the original balance at regular intervals. Understanding how contributions, time and yield interact lets you transform an abstract target into a practical schedule. It also reveals the hidden cost of delaying deposits, because lost compounding time cannot be repurchased later.
This calculator models three common money-management questions. First, it estimates how many months you need to hit a chosen goal when you deposit a fixed amount each month. Second, it reverses the equation to find the contribution required within a set timeframe. Third, it projects the balance at a future date.
Use it to translate a dream vacation fund, education fee, or retirement target into a concrete timeline or monthly figure. Generated tables and charts help you visualise how principal, added contributions and earned interest jointly shape growth over the years. All figures assume constant returns and regular, on-time deposits; actual market performance may vary.
Money placed in an interest-bearing account grows because each new period adds returns to both the opening balance and any deposits made during that interval. The process is multiplicative: future value depends on the compounding frequency, the periodic rate, the number of periods, and the size and timing of additional contributions. Solving for any one unknown—time, contribution, or ending balance—while holding the others constant yields the three operating modes of the calculator.
The reactive engine carries inputs through algebraic or iterative paths best suited to the requested mode. Iteration iteratively adds contributions and applies rate compounding until the goal threshold is crossed, whereas direct algebraic solutions isolate the contribution term with closed-form equations. A lightweight charting layer then visualises the resulting schedule.
| Symbol | Meaning | Unit | Typical Range | Sensitivity |
|---|---|---|---|---|
| opening balance | $ | 0 – 1 000 000 | linear | |
| periodic contribution | $/month | 0 – 10 000 | high | |
| period rate | decimal | 0 – 0.02 | exponential | |
| number of periods | months | 1 – 600 | exponential | |
| goal amount | $ | 1 000 – 5 000 000 | linear |
Starting with $10 000 and adding $500 each month at 5 % nominal annual interest compounded monthly for three years yields an estimated $30 991.39. The calculation substitutes =0.05/12 and =36 into the first formula, sums the geometric series, and rounds to cents.
Algebraic paths run in constant time O(1). Iterative simulations scale linearly with periods O(n) but remain sub-millisecond for decade-long horizons on mainstream browsers. Double-precision floats guard against rounding drift under typical consumer rates. The component exports CSV directly in the browser, and the charting layer reflows on window-resize events without blocking.
Follow this flow to obtain reliable projections:
Interest equals all earnings attributed to the periodic rate; it excludes your own deposits, which appear separately as contributions.
Yes. Monthly, quarterly, semi-annual, and annual compounding frequencies reflect common banking schedules and affect growth speed.
No. All inputs remain in your browser; nothing is transmitted, saved, or shared.
Outputs round to two decimals. Minor differences can arise from bank-specific day-count conventions or rounding policies.
The cap prevents accidental infinite loops and reflects a 50-year horizon, long enough for typical financial planning.