Interest Calculator
Estimate how much interest your savings will earn over time with compounding and optional periodic contributions.
Reviewed by the CalcCafe editorial team · Last updated 1 July 2026 · How we test our tools
Example
Start with $10,000 at 5% annual interest, adding $200/month for 10 years with monthly compounding (contributions at end of period).
After 120 months the balance grows to $47,526.55. You deposited $10,000 + $24,000 in contributions = $34,000, so you earned $13,526.55 in interest.
How it works
Enter your starting principal, annual interest rate, time horizon, contribution amount, and how often interest compounds. The calculator grows the principal and each contribution with compound interest and updates live.
Good to know
This Interest Calculator projects how a lump sum plus a steady stream of deposits grows when compound interest is applied. You enter a starting principal, an annual rate, a number of years, a recurring contribution, and how often interest compounds, and it returns the end balance along with a breakdown of total interest, total contributions, and total deposited. It is built for savers, CD and high-yield savings shoppers, and anyone wanting to see the long-run effect of "set it and forget it" deposits without building a spreadsheet.
Reach for it when you want a quick what-if: comparing a one-time deposit against a smaller deposit topped up monthly, testing whether monthly versus annual compounding meaningfully changes the outcome, or sanity-checking a bank's quoted growth figure. Because the math runs live in your browser as you type, it is fast to nudge a single input and watch the end balance move.
Read the result by separating what you put in from what the rate earned. "Total deposited" is principal plus every contribution (your own money), and "Total interest" is everything above that. The three bars show the proportion of the final balance coming from principal, contributions, and interest, which makes it easy to see when compounding starts doing the heavy lifting over long horizons.
One caveat to keep in mind: this tool assumes contributions happen at the same frequency you select for compounding, and that the rate and contribution stay fixed for the whole term. Real accounts often have variable rates, fees, or taxes on interest, so treat the figure as a clean baseline rather than a guaranteed outcome. Switching contribution timing to "Start of period" gives each deposit one extra compounding cycle, which nudges interest slightly higher.
Frequently asked questions
Does this account for the money I add over time?
Yes. Each periodic contribution is treated as a deposit that then earns compound interest for the remaining time. You can also choose whether contributions land at the start or end of each period, which slightly changes the interest earned.
What does the compounding frequency setting do?
It sets how often interest is added to your balance and how often you contribute. More frequent compounding (e.g. monthly vs. annually) earns slightly more interest at the same annual rate because earned interest starts compounding sooner.
Is my data uploaded anywhere?
No — this calculator runs entirely in your browser; nothing is uploaded.
Is this financial advice?
No. These are educational estimates — consult a qualified financial professional before making decisions.
People also ask
What is the difference between simple and compound interest?
Simple interest is calculated only on the original principal, so it grows in a straight line. Compound interest is calculated on the principal plus previously earned interest, so the balance accelerates over time. This tool uses compound interest.
Does contributing at the start of the period really earn more than the end?
Yes, slightly. A start-of-period deposit sits in the account one extra compounding cycle before the next interest is applied, so it earns a little more over the full term. The longer the horizon and the higher the rate, the larger that gap becomes.
What annual interest rate should I enter?
Use the rate your account or investment actually quotes, such as a savings APY or an assumed average return. For neutral planning, many people test a range of conservative and optimistic rates to see how sensitive the outcome is.
How do I figure out how long it takes to double my money?
A common shortcut is the Rule of 72: divide 72 by the annual interest rate to estimate the years to double. For example, at 6% it takes roughly 12 years. It is an approximation, not an exact figure.
Is the interest this calculator shows taxable?
In many jurisdictions interest earned in a standard account is treated as taxable income, while tax-advantaged accounts may defer or exempt it. This calculator does not deduct taxes, so the interest figure is pre-tax. Check your local rules for specifics.
Why does monthly compounding give a higher balance than annual at the same rate?
With more frequent compounding, earned interest is added to the balance sooner and begins earning its own interest earlier. At the same stated annual rate, that produces a higher effective yield and a larger end balance.
Can I use this to plan regular savings deposits like a monthly transfer?
Yes. Enter your recurring amount in the contribution field and choose the matching frequency, and the tool grows each deposit with compound interest for its remaining time. It assumes the contribution stays constant for the entire term.
How much is 5% interest on $10,000?
5% interest on $10,000 is $500 for one year, since 10,000 × 0.05 = $500. With monthly compounding at a 5% annual rate the first year earns slightly more, about $512, because each month's interest starts earning interest itself. Over 10 years with no additional deposits, $10,000 at 5% compounded monthly grows to about $16,470, so roughly $6,470 of interest.
How do I calculate how much interest?
For one year, multiply the balance by the annual rate as a decimal: $30,000 at 4% earns 30,000 × 0.04 = $1,200. For longer periods with compounding, use balance × (1 + rate ÷ n)^(n × years), where n is the number of compounding periods per year, then subtract the starting balance to isolate the interest. If you also make regular deposits, each deposit compounds for a different length of time, which is what this calculator handles for you.
How much interest does $30,000 earn in a year?
It depends entirely on the rate. At 1% it is 30,000 × 0.01 = $300; at 4% it is $1,200; at 5% it is $1,500. With monthly compounding those figures rise slightly, for example about $1,535 at 5%. Savings rates vary by bank and change with the market, so plug your actual APY into the calculator.
How much interest will I earn on $500,000 in a year?
At 4% you would earn 500,000 × 0.04 = $20,000 in a year, and at 5% you would earn $25,000, before tax. With monthly compounding the totals are a bit higher, about $20,371 at 4% and $25,581 at 5%. Interest earned in a regular savings account or CD is taxable as ordinary income, so the after-tax amount is smaller. Rates vary by bank and over time, so use the APY you are actually offered.
Can I live off the interest of $500,000?
Only with a modest budget. At 4% interest, $500,000 produces about $20,000 a year, or roughly $1,667 a month before tax, and at 5% about $25,000 a year. Interest rates move, so income that looks comfortable at 5% could fall sharply if rates drop, and inflation slowly erodes the purchasing power of both the interest and the principal. Most people would combine the interest with Social Security, a pension or other income rather than relying on it alone; this is general information, not advice.
How much money do I need to invest to make $3,000 a month?
You need $36,000 a year, so divide that by the yield: at 4% you need 36,000 ÷ 0.04 = $900,000, at 5% you need $720,000, and at 6% you need $600,000. A higher yield means a smaller lump sum, but higher-yielding investments generally carry more risk or lock your money up longer. These figures are before tax and do not account for inflation, so the income would buy less over time. This is general information, not investment advice.
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Sources & references
These tools follow our methodology and provide educational estimates only — verify important figures with a qualified professional.