Compound Interest Calculator

Compound Interest Calculator: Project growth with recurring contributions and compounding frequency. It's built around investment, compound, interest, so you can go from a raw question to a checked answer without switching tools.

The math behind it: P is the starting balance, C is the contribution per period, r is the annual rate, n is the number of compounds per year, and t is the number of years invested. The core relationship is FV = P(1 + r/n)ⁿᵗ + C × [((1 + r/n)ⁿᵗ − 1) ÷ (r/n)], shown above the calculator so you can see exactly how your inputs turn into the result.

To use it well: (1) Enter your starting balance and the contribution you plan to add each period. (2) Provide the annual return rate, years invested, and compounding frequency. (3) Scan the projection to compare total contributions versus growth generated by compounding. Keep your units consistent as you go, and re-run a case you already know the answer to — it's the fastest way to catch a typo before it throws off a result you're relying on.

Worked example: entering Initial deposit = $10,000, Contribution = $200 monthly, Rate = 7%, Years = 15, Compounding = Monthly returns Future value ≈ $91,881.93 (Growth ≈ $45,881.93 over $46,000 contributed). Try swapping in your own numbers next, especially a case you're unsure about, before you use this for something that matters.