OnSumoTools

Compound interest calculator (2026)

Model contributions, rate, and time with instant feedback and a clear growth chart.

100% client-side. Your inputs stay in this browser.

Choose your region first, defaults and scales update for that location. Adjust sliders to model your scenario.

Changing region applies typical local defaults (amounts, rate, horizon) so projections match that market, same compound-interest math everywhere.

Future value

$343,778

Total contributed

$130,000

Interest earned

$213,778

Multiplier

2.64×

$10,000
$500
8.0%
20

How does the Compound Interest Calculator work step by step?

This compound interest calculator is updated for 2026 savings and investment scenarios. It applies the standard future value formula for periodic contributions: FV = P x (1 + r/n)^(n x t) + PMT x (((1 + r/n)^(n x t) - 1) / (r/n)), where P is your starting principal, PMT is the periodic contribution, r is the annual rate as a decimal, n is compounding frequency per year, and t is years. Monthly compounding (n = 12) means interest is calculated and added twelve times per year; each addition raises the base for the next calculation, producing the exponential curve in the chart. The gap between total balance and total contributed is interest earned: money that came from compounding, not from your deposits.

What does a typical Compound Interest Calculator result look like?

Starting conditions: $10,000 initial deposit, $500 per month added, 8% annual return, monthly compounding, 20 years. Result: approximately $343,778. Total contributed: $130,000 ($10,000 plus $500 times 240 months). Interest earned: approximately $213,778. Multiplier: 2.6x total contributions. To check rate sensitivity, change 8% to 7%: the 20-year result drops by roughly $60,000, more than 2 years of contributions wiped out by a single percentage point.

Learn the compound interest calculation

Read the compound interest formula guide for the variables and calculation steps, then compare compound interest with simple interest to see how interest on prior interest changes growth over time.

Frequently asked questions

  • How does compounding frequency affect my balance?

    More frequent compounding means interest is added to your balance more often, and each subsequent calculation starts from a slightly higher number. At 8% annual rate, daily compounding produces about 0.03% more per year than monthly compounding. Over 30 years, that difference on a large balance becomes noticeable but is not the primary driver of growth.

  • What annual return rate should I use?

    7% is the approximate inflation-adjusted historical return of US equities based on Aswath Damodaran's annual dataset (NYU Stern). The nominal historical average before inflation is closer to 10%. Use 7% for a conservative real-return model and 10% for a nominal model. Neither is a forecast, and your actual returns will depend on asset allocation, fees, and timing.

  • Does this account for taxes on interest?

    No. The calculator shows gross growth before any tax impact. For taxable brokerage accounts, a common approach is to multiply your expected return by one minus your marginal tax rate to estimate after-tax growth. For tax-advantaged accounts like a 401(k) or IRA, the gross figure is more applicable since taxes are deferred or eliminated depending on the account type.

  • What does the multiplier number mean?

    The multiplier is future value divided by total contributions. A multiplier of 2.6x means every dollar you deposited grew to $2.60 by the end of the period. The extra $1.60 per dollar came entirely from compounding returns, not from additional contributions. Higher rates, longer horizons, and more frequent contributions all push the multiplier higher.

  • Why does starting earlier matter so much?

    Compound growth is exponential, not linear. Each year the growth is calculated on a larger base, so the absolute dollar gains accelerate over time. The final years of a long horizon generate more nominal growth than all the early years combined. Starting five years earlier does not add roughly 25% to the outcome; depending on the rate and horizon it often adds 50% or more.

  • Is this calculator accurate for 2026?

    Yes. The compound interest formula is a mathematical constant, not tied to tax law or policy changes. The FV formula this tool uses does not change year to year. What changes is the rate you input: for 2026, high-yield savings accounts are offering rates in the 4-5% range, while the historical inflation-adjusted return on US equities remains around 7% per year based on long-run data. Enter the rate that matches your actual account or investment to get an accurate projection.

  • What is the average compound interest rate in 2026?

    It depends on the account type. As of 2026, high-yield savings accounts from online banks are offering roughly 4-5% APY. US money market funds are in a similar range. The long-run nominal average for a diversified US equity index is approximately 10% per year; the inflation-adjusted (real) return is approximately 7%, based on historical data compiled by NYU Stern. Rates vary by institution and market conditions, so verify current rates with your bank or brokerage before building a long-term projection.

Related tools

Interest on your interest

Simple interest pays you only on what you put in. Compound interest pays on what you put in plus everything it has already earned. Over a few months you barely notice. Over thirty years it's the whole story.

Move the sliders for your starting amount, monthly deposits, rate and time. The chart redraws live, so you can see how each change plays out.

How often it compounds

Interest can be added yearly, monthly or daily. More frequent compounding gives a slightly higher balance, because earned interest starts earning sooner. The jump from yearly to monthly is visible. The jump from monthly to daily is small.

Rate matters far more than frequency. A one-point change in the return does more than any compounding schedule.

Picking a realistic rate

Don't plug in a number because it looks nice. A savings account pays far less than a stock fund has returned on average over long stretches, and stocks can drop in any given year. Think in ranges and run a low, middle and high case.

Today's actual rates change. Check what your bank or provider offers right now rather than trusting a number you read last year.

Start early

Time beats size. Someone who invests a modest amount from age 25 can end up with more than someone who invests double from age 40. The multiplier in the results shows how many times your total contributions have grown. Run the same plan with a ten-year-later start and compare.

What it leaves out

Taxes aren't included. Interest and gains may be taxed depending on the account type and where you live. Inflation isn't included either, so a balance in thirty years buys less than the same number buys today. For a real-terms view, use a lower rate that has inflation already taken off.

You can save your inputs locally in your browser if you want to come back to them. Nothing is sent to a server.