Compound interest calculator
See how your savings or investments could grow over time with compound interest. Add a starting amount, interest rate, term, compounding frequency and optional monthly contributions to project the future value and the interest earned.
How to use Compound Interest Calculator
- 1
Enter your starting amount
Add the initial sum you're investing or saving, and any monthly contribution.
- 2
Set the rate and term
Enter the annual interest rate and the number of years.
- 3
Choose compounding frequency
Pick yearly, quarterly, monthly or daily compounding.
- 4
Read the projection
See the future value, the total invested and the interest earned.
The power of compound interest
Compound interest is often called the most powerful force in finance, and for good reason: it is interest earned not just on your original money but on the interest that money has already earned. Over time this snowball effect can turn modest, steady saving into a surprisingly large sum, because each period's growth becomes the base for the next period's growth. The catch is that compounding is hard to picture in your head — the curve is not a straight line, and small changes in rate or time produce outsized differences decades later. This calculator makes the effect concrete. You enter a starting amount, an annual interest rate and a number of years, and it projects the future value, showing you the result that compounding produces rather than leaving you to guess. Seeing the number is genuinely motivating, and it makes the abstract idea of 'letting your money grow' into something specific you can plan around, compare and aim for.
Add regular contributions
For most people, real wealth is not built from a single lump sum but from a starting amount plus steady contributions over many years, so this calculator lets you include a monthly contribution. This reflects how saving and investing actually work: you put money in regularly, and each deposit then compounds for the rest of the term. The effect of these ongoing contributions is enormous over long periods, often dwarfing the starting amount, and the calculator captures it so your projection matches a realistic saving plan rather than an unrealistic one-time deposit. You can see how much difference adding a little more each month makes, or how a consistent contribution over a long horizon builds up. This is exactly the kind of what-if that helps with real decisions — whether it is worth increasing a monthly transfer to a savings or investment account, or how much you would need to contribute to reach a target by a certain date.
Compounding frequency and time horizon
Two factors quietly shape how much compound interest delivers: how often the interest compounds, and how long you leave the money to grow. This calculator lets you set both. You can choose whether interest compounds yearly, quarterly, monthly or daily, and see how more frequent compounding produces a slightly higher result for the same rate, because interest starts earning interest sooner. More importantly, you control the number of years, and adjusting it reveals the single biggest lever in compounding: time. Because growth accelerates, the difference between, say, twenty and thirty years is far larger than the difference between ten and twenty. Being able to slide the time horizon and watch the future value respond drives home why starting early matters so much, and why patience is rewarded. Seeing these factors interact — rate, frequency, contributions and especially time — turns the calculator into a tool for understanding how saving works, not just a box that prints one number.
See growth versus what you put in
A projection is most useful when it separates the money you contributed from the money your investment earned, and this calculator does exactly that. Alongside the projected future value, it shows the total amount you invested — your starting sum plus all your contributions — and the interest earned, which is the difference between the two. This breakdown is illuminating because it reveals how much of your final balance is your own money versus growth that compounding generated for you. Early on, most of the balance is what you put in; over a long horizon, the earned interest can come to rival or exceed your contributions, which is compounding's whole promise made visible. Seeing the three figures together helps you appreciate the return your money is working to produce and keeps your expectations grounded in the actual contribution required. It is the difference between a single impressive-looking total and a genuine understanding of where that total comes from and what it took to build it.
A projection, not a guarantee
It is worth being clear about what this calculator does. It projects growth using a fixed interest rate compounded over time, which is the right model for a savings account or for illustrating how compounding works. Real investments, however, do not deliver a smooth, fixed return: markets rise and fall, rates change, and actual results vary year to year. The calculator also does not account for taxes, fees or inflation, all of which affect what your money is really worth in the end. So the figure it produces is best treated as an illustration of the compounding principle and a planning aid, not a promise of a specific outcome. Used that way it is genuinely valuable — it helps you compare scenarios, set savings targets and understand the impact of rate, time and contributions — while you keep in mind that a real investment's path will be bumpier. Everything is calculated privately in your browser, so you can model your plans without sharing your financial details with anyone.
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