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Investment Calculator
Project how a lump-sum investment plus regular contributions grows over time with compound interest. This investment calculator gives you numbers you can actually trust — enter a starting amount, a monthly contribution, an expected annual rate of return, and a time horizon to see your ending balance, total contributions, and total growth, broken down year by year.
The essentials
Four calculators, zero fluff
How the investment calculator works
This investment calculator projects the future value of your money using the compound interest formula, the same math used by savings accounts, index funds, and retirement accounts to grow a balance over time. You provide four inputs: an initial investment (which can be zero), a regular contribution, an expected annual rate of return, and a time horizon in years. Used as a simple investment growth calculator, it shows how a lump sum compounds on its own; used as an investment calculator with monthly contributions, it also credits every deposit with its own share of the growth from the day it's added. Because gains earn their own gains in later periods, growth accelerates over time even without adding more money — the core idea behind compounding.
The compound interest formula
The baseline formula for compound interest without contributions is A = P(1 + r/n)^(nt), where A is the ending balance, P is the initial principal, r is the annual interest rate as a decimal, n is the number of times interest compounds per year, and t is the number of years invested. When you add regular contributions, each deposit is treated as its own smaller principal that compounds for whatever time remains until the end of the horizon, and the calculator sums all of those pieces together with the growth on the original principal. Compounding monthly instead of annually at the same stated rate produces a modestly higher ending balance, because gains are locked in and start earning their own return sooner — and time matters even more, since doubling your time horizon more than doubles your ending growth at a fixed rate.
How much will my investment be worth?
As an investment return calculator, this tool doesn't just spit out one number — it separates your ending balance into total contributions and total growth, so you can see exactly how much of your future balance came from what you put in versus what the market did for you. It also works as a compound interest investment calculator: because interest compounds on interest already earned, small differences in rate of return compound into large differences over long time horizons. To see what that balance is worth after rising prices, use it as an investment calculator with inflation by entering a real, inflation-adjusted rate of return instead of a nominal one.
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Full transparency
Every calculator shows its year-by-year breakdown — principal, interest, and balance — not just a final number.
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Built for real decisions
Adjust extra payments, contribution frequency, and compounding to model the choice you're actually facing.
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Instant, no clutter
Everything runs client-side as you type. No accounts, no waiting, no popups between you and your answer.
Rate-of-return benchmarks
The rate of return you assume has an outsized effect on the projection, so it's worth grounding it in historical benchmarks rather than guessing. Broad U.S. stock market indexes like the S&P 500 have returned close to 10% annually on average over long multi-decade periods before inflation, or roughly 7% after adjusting for inflation. A diversified portfolio of investment-grade bonds has historically returned in the neighborhood of 4-5% annually, with much less volatility than stocks. Cash-equivalent vehicles — high-yield savings accounts, money market funds, and short-term CDs — tend to track close to prevailing short-term interest rates. A common approach is to model a lower, more conservative rate for near-term goals and a higher rate for long-term goals where there's more time to recover from down years. None of these figures are guarantees: actual market returns vary substantially from year to year.
Frequently asked questions
How do I calculate compound interest on an investment?
Compound interest grows a balance by applying a rate of return to the principal plus any interest already earned. The formula is A = P(1 + r/n)^(nt), where P is the starting principal, r is the annual rate as a decimal, n is the number of compounding periods per year, and t is the number of years. Regular contributions add to the balance before each compounding period, so they earn returns too.
What is a good annual rate of return to assume?
The S&P 500 has historically returned close to 10% annually before inflation, and roughly 7% after adjusting for inflation, over long multi-decade periods. A diversified bond portfolio has historically returned around 4-5%, and high-yield savings accounts and CDs typically track close to short-term interest rates. These are historical averages, not guarantees, and actual returns vary significantly year to year.
How often should interest compound for the most accurate estimate?
Most brokerage and retirement accounts effectively compound daily or monthly as gains are reinvested, so monthly compounding is a reasonable default for most long-term projections. Daily compounding produces a slightly higher result than annual compounding at the same stated rate, but the difference is usually small compared to uncertainty in the rate of return itself.
Does this investment calculator account for taxes or inflation?
By default, no — it projects nominal growth based on the rate of return, contribution amount, and time horizon you enter, without deducting taxes or account fees. To use it as an investment calculator with inflation, enter an inflation-adjusted (real) rate of return instead of a nominal one to see your ending balance in today's purchasing power.
What's the difference between an investment calculator and a savings calculator?
The math is the same compound growth formula either way. The distinction is mostly about the rate of return assumed: savings calculators typically use low, stable rates similar to a bank account, while investment calculators are used with higher, more variable rates typical of stocks, funds, or other market-based assets.
Whether you're mapping out a first brokerage account or stress-testing a retirement plan, this investment calculator lays out the full year-by-year picture instead of a single guess — so you always know how much your investment could be worth, and why.