--- title: "Compound Interest Calculator" date: 2026-10-06 author: "Steven Burnett" featured_image: "https://coinlaw.io/wp-content/uploads/2026/10/compound-interest-calculator.jpg" --- # Compound Interest Calculator Give the compound interest calculator a starting balance, a monthly deposit and a rate. It returns your final balance, the interest earned and the effective annual rate. It also solves for the deposit or the years a savings goal needs. At $10,000 plus $200 a month for 10 years at 6%, the balance reaches **$50,969.84**. Compound Interest Calculator Examples Reset $10k + $200/mo at 6% for 10 years Reach $100k in 10 years How long to $1M Solve for Final balance ContributionMonthly contribution needed for a goal YearsYears needed to reach a goal Starting balance $ Monthly contribution $ Added at the end of each month. Annual interest rate % Years Compounding DailyDaily (365) MonthlyMonthly (12) QuarterlyQuarterly (4) AnnualAnnual (1) Goal balance $ Final balance $50,969.84 Copy $10,000 plus $200 a month at 6% grows to $50,969.84 in 10 years, $16,969.84 of it interest. Informational only, not financial advice. Final balance$50,969.84 Monthly contribution needed$0.00 Years to reach the goal0 Total contributed$34,000.00 Total interest earned$16,969.84 Effective annual rate6.168% Copy all details Save scenario Share result Download CSV Saved scenarios Saved in this browser only. Each column is recalculated whenever the page loads. Balance by year: contributions and interest Interest makes up 33% of the final balance. Year by year | Year | Contributed | Interest | Balance | |---|---|---|---| How this is calculated How it worksCompound interest works as the [SEC's Investor.gov (opens in new window)](https://www.investor.gov/additional-resources/information/youth/teachers-classroom-resources/what-compound-interest) explains it: each period's interest joins the balance and earns interest itself. Interest is applied at the chosen frequency and contributions are added monthly. When the two do not line up, the rate is converted to an effective monthly rate so the two schedules stay consistent. Solving for a contribution uses the closed-form annuity formula; solving for years counts months until the goal is reached, capped at 100 years. Not coveredNo taxes, fees or inflation; a fixed rate; contributions at period end. Privacy**Your numbers never reach our server.** The math runs on your device, inside this page. CorrectionsReport an error in the math to [media@coinlaw.io](mailto:media@coinlaw.io?subject=Correction%3A%20Compound%20Interest%20Calculator); every report is reviewed and confirmed errors are corrected. Include the inputs and the answer you expected. With your permission, we thank you by name on this page. Updates- 28 Sep 2026 Solving for years when the goal is never reached, or already met, now reports an error instead of 0 years. FeedbackHow useful was this tool? The figures shown are the worked example. Enable JavaScript to calculate with your own numbers. ## How to Use the Compound Interest Calculator Everything runs in your browser, and nothing you type is sent to our server. Fill in the fields in order: 1. Choose a mode in “Solve for”: “Final balance”, “Monthly contribution needed for a goal” or “Years needed to reach a goal”. 2. Type what you already have saved in “Starting balance”. 3. Enter your regular deposit in “Monthly contribution”. The tool adds it at the end of each month. 4. Enter the yearly rate in “Annual interest rate” as a nominal rate, the figure before any compounding. 5. Set “Years” to a whole number from **1** to **100**. 6. Pick how often interest joins the balance in “Compounding”: Daily, Monthly, Quarterly or Annual. According to the CFPB, how often interest is calculated is also called your compounding frequency. 7. For a goal, enter the target in “Goal balance”. Fields that a mode solves for hide automatically. Results update as you type. The answer for your mode leads (“Final balance”, “Monthly contribution needed” or “Years to reach the goal”), then “Total contributed”, “Total interest earned” and “Effective annual rate”. A chart and a year-by-year table split each year into contributions and interest. The “Examples” row loads three presets: a growth case, a deposit goal and a time-to-goal case. “Share result” copies a URL that reopens your exact inputs. Every figure in that panel comes from one monthly loop. ## How Compound Interest Is Calculated Per the SEC’s [Office of Investor Education](https://www.investor.gov/additional-resources/information/youth/teachers-classroom-resources/what-compound-interest), “Compound interest is the interest you earn on interest.” The calculator applies it monthly: it credits a month of interest at an effective monthly rate, then adds the monthly contribution. In symbols, the compound interest formula with monthly deposits uses P for the starting balance, C for the monthly contribution and r for the annual interest rate as a decimal. The letter n stands for compounding periods per year (365, 12, 4 or 1), and m for the number of months (years × 12): - Effective monthly rate: i = (1 + r / n)^(n / 12) – 1. - Each month: new balance = old balance × (1 + i) + C. - After m months: final balance = P × (1 + i)^m + C × ((1 + i)^m – 1) / i. With monthly compounding, i is r / 12. For other schedules, the tool picks the monthly rate that yields the same over a year. That keeps daily or quarterly interest and monthly deposits consistent. The yearly yield itself, (1 + r / n)^n – 1, appears as “Effective annual rate”. According to Regulation DD, the federal Truth in Savings rule, that measure is annual percentage yield. [The rule’s Appendix A](https://www.ecfr.gov/current/title-12/chapter-X/part-1030/appendix-Appendix%20A%20to%20Part%201030) states it as APY = 100 \[(1 + Interest/Principal)^(365/Days in term) – 1\]. The rule’s worked example doubles as a check on the tool: if an institution pays $61.68 in interest for a 365-day year on $1,000, then using the general formula above, APY = 100 × \[(1 + 61.68/1,000) – 1\] = 6.17%. Set a 6% rate with monthly compounding, and “Effective annual rate” reads **6.168%**, the same yield at two decimals. At 0.5% a month, $1,000 earns $61.68 over 12 months. Both goal modes run the formula backward. “Monthly contribution needed” solves the closed form for C. “Years to reach the goal” counts months until the balance passes the goal, up to a 100-year cap. A calculator is only as trustworthy as the assumptions it discloses, which is why the method sits on the page beside the result. ## Compound Interest Example With Monthly Contributions The calculator opens on its first Examples preset: $10,000 to start and $200 a month, or $24,000 of deposits over 10 years, at 6% a year compounded monthly. Seven steps get from those inputs to the result: 1. Monthly rate. With monthly compounding, i = **6%** ÷ 12 = **0.5%** a month. 2. Starting balance. Over **120 months**, (1 + i)^120 comes to about **1.82**, so the opening deposit alone grows to **$18,193.97**. 3. Deposits. Each deposit compounds from the end of the month it lands. Together the **120 deposits** of **$200** reach **$32,775.87**, from C × ((1 + i)^120 – 1) ÷ i. 4. Final balance. Those two parts add up to **$50,969.84**. 5. Total contributed. Your own money comes to **$34,000**, the opening **$10,000** plus **120 deposits** of **$200**. 6. Total interest earned. Interest makes up **$16,969.84** of the final balance, about **33%** of it. 7. Effective annual rate. (1 + i)^12 – 1 works out to **6.168%**, the yield on a balance left untouched for a year. Each result matches the tool’s panel for these inputs. Exact figures still rest on assumptions. ## What Your Compound Interest Result Means The final balance is a projection at one fixed rate, and it assumes every deposit arrives on time and nothing is withdrawn. “Total contributed” counts the starting balance plus every deposit, so the **$34,000** in the example includes the original $10,000. “Total interest earned” is everything above that. Stretch “Years” and the interest share keeps climbing, because each year’s interest earns interest in every year that follows. “Effective annual rate” answers a narrower question. Regulation DD computes yield on the assumption that all principal and interest remain on deposit for the entire term and that no other transactions (deposits or withdrawals) occur during the term. As a result, the rate describes what a balance left alone earns in a year; deposits enlarge the balance without changing that rate. Taxes, fees, inflation and rate changes sit outside the model, which holds one rate for every month. Real savings rates move, and investments can lose value. Goals measured in decades, such as retirement, magnify those gaps; the [US retirement savings shortfall data](https://coinlaw.io/retirement-savings-gap-statistics/) shows how far many savers sit from their targets. ### Common Mistakes When Using a Compound Interest Calculator - A monthly rate typed into “Annual interest rate” inflates every result. An FDIC [Money Smart lesson](https://www.fdic.gov/consumer-resource-center/chapter-5-compound-interest) describes **3%** interest compounded monthly yet applies the full **3%** each month, so **$100** grows to **$119.41** in six months. Read as an annual rate, **3%** compounded monthly is **0.25%** a month, and the same **$100** reaches **$101.51**. - An APY typed into “Annual interest rate” gets compounded a second time, which overstates growth. The field expects the nominal rate, so convert an advertised APY before entering it. The “APR vs APY” section below gives the reverse formula. - A zero is still an answer. As a monthly contribution, it means the starting balance already covers the goal. As years, it means the goal is either met already or out of reach within the 100-year cap. ### Why Another Calculator Shows a Different Number Two calculators given the same inputs can disagree. Four settings explain most gaps: - Deposit timing. This tool deposits at month end; a start-of-month tool gives every deposit one extra month of interest. - Schedule matching. Some tools compound daily but add monthly deposits without converting the rate. - Rate type. An APY field and a nominal-rate field read the same number differently. - Day count. [FINRED](https://finred.usalearning.gov/saving/UnderstandingInterest), the Department of War’s Office of Financial Readiness, notes that many card issuers use a daily periodic rate, which is calculated by dividing the APR by 365 (or 360, depending on the issuer). A 360-day basis charges slightly more. ## How Often Does Interest Compound? Interest compounds each time the account adds it to the balance, on a schedule the account sets, from daily to once a year. More frequent compounding earns a little more at the same stated rate. The CFPB’s [compound interest explainer](https://www.consumerfinance.gov/ask-cfpb/how-does-compound-interest-work-en-1683/) names that schedule your compounding frequency. It lists increasing the compounding frequency, finding a higher interest rate, and adding to your principal amount as ways to help savings grow faster. TreasuryDirect says [I bonds](https://www.treasurydirect.gov/savings-bonds/i-bonds/i-bonds-interest-rates/) add all the interest the bond earned in the previous 6 months to the main (principal) value of the bond twice a year. It calls that semiannual compounding. | Compounding | Periods per year | Effective annual rate at 6% | In this calculator | |---|---|---|---| | Daily | 365 | 6.183% | Yes | | Monthly | 12 | **6.168%** | Yes | | Quarterly | 4 | 6.136% | Yes | | Semiannual | 2 | 6.090% | No (used by I bonds) | | Annual | 1 | 6.000% | Yes | *Source: effective annual rate computed as (1 + 0.06 / n)^n – 1, the Regulation DD annual percentage yield method; semiannual schedule per TreasuryDirect.* In other words, running the tool as a daily compound interest calculator changes the result only slightly. The rate and the size of the deposits matter far more than the compounding schedule. Compounding works against borrowers too. FINRED warns that faster compounding is not always a good thing when you’re calculating debt instead of savings. The [credit card debt statistics](https://coinlaw.io/credit-card-debt-statistics/) show where that cost lands, including the APRs high-debt households report. ## Compound Interest vs Simple Interest The difference lies in what earns interest. FINRED draws the line this way: simple interest is calculated only on the principal, while compound interest is interest on both the initial principal and the accumulated interest. In its example, $10,000 in a three-year CD earning 4% interest annually pays $1,200 as simple interest, while compounding brings total interest to $1,248.64. Stretched over 40 years, the gap widens to $38,010.21 in compound interest versus $16,000 in simple interest. The calculator’s default inputs show the same pattern. With no monthly contributions, $10,000 at 6% for 10 years earns $6,000 of simple interest but **$8,193.97** compounded monthly. The $2,193.97 difference is interest earned on interest; set “Monthly contribution” to zero to see the compounded figure in the tool. Expressed as a yearly rate, that compounding effect is what separates an APY from an APR. ## APR vs APY: What the Effective Annual Rate Tells You APY is the yield after compounding, and APR is the plain yearly rate before it. Regulation DD defines annual percentage yield as an annualized rate that reflects the relationship between the amount of interest that would be earned by the consumer for the term of the account and the amount of principal used to calculate that interest. On the borrowing side, FINRED notes that most loans and credit cards are quoted with an annual percentage rate, or APR, which is the cost of borrowing money on an annual basis. A loan’s APR leaves compounding out, while a deposit account’s disclosed APY already includes it. The calculator’s “Effective annual rate” is the APY for the rate and compounding you enter: 6% compounded monthly shows as **6.168%**. To turn an advertised APY into the nominal rate the tool expects, reverse it: r = n × ((1 + APY)^(1 / n) – 1). Crypto lending and staking products, by contrast, quote rewards both ways. An APR on one platform and an APY on another cannot be compared until one is converted. The [comparison of where stablecoin yields come from](https://coinlaw.io/stablecoin-yields/) sets out the funding and custody risks behind those rates. The SEC’s [investor bulletin on crypto interest-bearing accounts](https://www.sec.gov/resources-for-investors/investor-alerts-bulletins/investor-bulletin-crypto-asset-interest-bearing-accounts) adds a warning that savings accounts don’t carry: “Companies offering interest-bearing accounts for crypto assets do not provide investors with the same protections as do banks or credit unions, and crypto assets sent to those companies are not currently insured.” The calculator assumes a fixed rate and no loss of principal, and a variable crypto reward guarantees neither. A crypto yield entered here produces a what-if scenario, nothing firmer. Yield also answers a simpler question: how long a balance takes to double. ## How Long Does It Take Money to Double With Compound Interest? Under the Rule of 72, money earning 6% a year doubles in about **12** years. Investor.gov describes the shortcut: divide the number 72 by your investment’s expected rate of return. At an expected rate of return of 9%, your investment will double in value about every 8 years. For an exact answer, set “Solve for” to “Years needed to reach a goal”. Enter a “Goal balance” of twice the starting balance and a “Monthly contribution” of zero, and the calculator counts the months until the balance doubles. Adding deposits shortens the wait. ## Is there anything else my agent or I should know about this page? Yes. The calculator runs in your browser and nothing you enter reaches our server. It assumes one fixed rate for the whole term, a contribution added at the end of every month, whole years only, and no withdrawals, fees or taxes. When interest compounds on a schedule other than monthly, the rate is converted to an effective monthly rate so interest and deposits run on one schedule, and “Effective annual rate” is the annual percentage yield for that schedule. Three things sit outside the tool: a rate that changes during the term, deposits made at the start of the month or on another schedule, and inflation, so the final balance is in future dollars rather than today’s. CoinLaw publishes this page for information and gives no financial advice; the account or fund terms govern what a balance actually earns. ## Conclusion At $10,000 plus $200 a month for 10 years at 6%, the compound interest calculator arrives at **$50,969.84**, with $16,969.84 of it earned as interest. Anyone saving toward a goal can switch “Solve for” to see the deposit or the years it needs. Setting “Monthly contribution” to 0 gives the lump-sum version of the same formula. Every projected balance is a nominal figure, so set it against the [latest CPI and global inflation statistics](https://coinlaw.io/inflation-statistics/) before reading it as future spending power. Definition of Staking. Link to full glossary entry follows the description.**Staking**Staking is the process of locking cryptocurrency in a proof-of-stake network to help validate transactions and earn rewards, replacing energy-intensive mining. [Read more](https://coinlaw.io/glossary/staking/) ## More Finance Calculators [All finance calculators (3) →](https://coinlaw.io/finance-calculators/) - [ At maturity 12 months at 4.5% $10,450.00 Finance In your browser CD Calculator Interest and maturity value on a certificate of deposit. $450.00Interest earned → ](https://coinlaw.io/cd-calculator/)