Calculate simple and compound interest, find the rate you're earning or paying, compare savings accounts vs. CDs vs. loans, and see how much your money grows — all in real time.
💰 Simple & Compound🔍 Find Your Rate📊 Compare Rates🏦 Loan vs. Savings📅 APR vs APY
💰Interest
🔍Find Rate
📊Compare
🏦Loan vs. Save
📅APR vs APY
💰Interest Details
📐 Simple Interest: Calculated only on the original principal. Formula: I = P × R × T. Common in short-term loans and car loans.
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Optional regular deposit (compound mode only)
🔍Solve For Interest Rate
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For loans: total of all payments made. For savings: final account balance.
📊Amount & Term
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💳Rates to Compare
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National avg savings (2026)
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HYSA avg (Mar 2026)
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Best CD rate (Mar 2026)
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Varo HYSA top rate
🏦Your Loan
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Avg personal loan (2026)
💰Your Savings Alternative
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HYSA avg (Mar 2026)
📅Convert Between APR & APY
📌 APR is the stated annual rate. APY reflects actual return after compounding. APY is always ≥ APR.
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Total Interest Earned
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Enter details to calculate
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Daily Interest
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Interest accruing every day
🍩 Breakdown
📋 Summary
📊 Rate Comparison
📅 Year-by-Year Growth
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Balance
Interest Earned
Total Interest
📈 Growth Over Time
⚠️ Estimates for planning purposes only. Interest rates reflect US market averages as of March 2026. Compound interest calculations use standard formula A = P(1 + r/n)^(nt). APY/APR conversions per standard financial definitions. Actual returns depend on your specific institution and product. ✦ CatchyTools.com
What Is an Interest Rate Calculator?
An interest rate calculator is a financial tool that helps you understand how interest works across different scenarios — whether you're earning it on savings, paying it on a loan, or trying to figure out the actual rate you're getting on an account or debt. By entering your principal, rate, and time period, you instantly see your total interest, final balance, and how your money grows (or what it truly costs you).
Our calculator goes well beyond a basic tool. It handles both simple and compound interest with any compounding frequency, solves backwards to find an unknown rate, compares up to four different rates side-by-side, shows the true difference between a loan cost and savings alternative, and converts between APR and APY — all updating live as you type.
💡 Why it matters in 2026: The Federal Reserve's benchmark rate sits at 3.50%–3.75% as of March 2026. High-yield savings accounts are paying up to 5.00% APY, while the national average savings account yields just 0.60% APY. That gap — 4.40 percentage points — means a $50,000 savings balance earns $2,200 more per year at the top HYSA rate vs. a traditional bank. Knowing the exact math is the difference between leaving money on the table and making it work for you.
What Is Interest?
Interest is the cost of using someone else's money — or the reward for letting someone use yours. When you borrow money, interest is what you pay the lender for the privilege of using their funds over time. When you deposit or invest money, interest is what you earn as compensation for making your capital available.
Interest is typically expressed as an annual percentage rate (APR or APY) applied to a principal balance. It is the foundational concept behind virtually every financial product in existence: savings accounts, mortgages, credit cards, bonds, personal loans, car financing, and more.
Simple Interest
Simple interest is calculated only on the original principal — it never compounds. The formula is:
I = P × R × T
Where I = Interest, P = Principal, R = Annual Rate (as a decimal), T = Time in years. Simple interest is common in short-term personal loans, some auto loans, and certain government bonds. It's straightforward — and predictable.
Compound Interest
Compound interest is interest calculated on both the original principal and the interest already accumulated. Often called "interest on interest," it causes balances to grow exponentially over time. The formula is:
A = P(1 + r/n)^(nt)
Where A = final amount, P = principal, r = annual rate, n = compounding periods per year, t = years. Compound interest works in your favor when saving — and against you when borrowing. Einstein reportedly called it "the eighth wonder of the world," and for good reason: $10,000 at 5% compounded monthly for 30 years becomes $44,677 — more than 4× the original investment.
Current US Interest Rates (March 2026)
Understanding where rates stand today helps you benchmark what you're earning or paying against the market. Here's a snapshot of key rates:
Financial Product
Rate / APY (March 2026)
Fed Funds Rate (target)
3.50%–3.75%
National Avg Savings Account
0.60% APY
Best High-Yield Savings (HYSA)
4.00%–5.00% APY
Best CD Rate (1-year)
Up to 4.30% APY
30-Year Fixed Mortgage
6.29%–6.39% APR
15-Year Fixed Mortgage
5.71%–5.78% APR
Average Personal Loan
12.26% APR
Average Credit Card Rate
~27.9% APR
Federal Student Loan (Undergrad)
6.39% APR
Auto Loan (new car, 60 mo)
~7.0%–8.5% APR
APR vs. APY: What's the Difference?
APR (Annual Percentage Rate) is the simple stated rate without factoring in compounding. APY (Annual Percentage Yield) reflects the actual return you earn or pay after compounding is applied over a full year. APY is always equal to or higher than APR.
Savings accounts and CDs advertise APY — this is the true return you'll see in your balance.
Loans and credit cards advertise APR — which understates the true cost if interest compounds more than once per year.
A credit card at 27.9% APR compounding daily has an effective APY of approximately 32.1% — nearly 4.2 percentage points higher than advertised.
The conversion formula: APY = (1 + APR/n)^n − 1, where n is compounding periods per year. Use the APR vs APY mode in our calculator to convert instantly and see the dollar difference on any amount.
How to Use Each Calculator Mode
Simple & Compound Interest: Enter principal, rate, and time. Toggle between simple and compound, adjust compounding frequency, and add optional monthly contributions. See year-by-year growth in the table.
Find Your Rate: Enter what you started with, what you ended up with (or will repay), and the time period — the calculator solves for the implied annual rate. Great for evaluating whether an offer is actually competitive.
Compare Rates: Enter up to four rates and see exactly how much difference each makes on the same principal over the same period. Side-by-side cards show the winner instantly.
Loan vs. Save: A unique mode that answers the perennial question — should you pay off debt or keep your savings? Enter your loan's cost and your savings account's return to see the net math.
APR vs APY: Convert in either direction, choose your compounding frequency, and see exactly how the gap widens on larger balances.
The Power of Compound Frequency
All else equal, more frequent compounding means more interest earned (or owed). On $10,000 at 5% for 10 years:
Compounding Frequency
Final Balance
Total Interest
Annually
$16,288.95
$6,288.95
Quarterly
$16,436.19
$6,436.19
Monthly
$16,470.09
$6,470.09
Daily
$16,486.65
$6,486.65
The difference between annual and daily compounding on $10,000 is ~$198 over 10 years — modest for small balances, but meaningful at $100,000 or over a 30-year horizon.
More Financial Calculators You'll Find Useful
Interest rate decisions don't happen in isolation. These tools from CatchyTools.com help you see the full picture:
Simple interest is calculated only on the original principal, so the interest amount stays constant each period. If you deposit $10,000 at 5% simple interest for 3 years, you earn $500/year — exactly $1,500 total. Compound interest is calculated on the principal plus all previously accumulated interest, so each period's interest grows the base for the next. The same $10,000 at 5% compounded monthly for 3 years earns approximately $1,614 — $114 more, and the gap widens exponentially over longer periods. For borrowers, compound interest is why credit card debt feels impossible to pay off — you're paying interest on interest every billing cycle.
As of March 2026, the national average savings account APY is just 0.60% — but the best high-yield savings accounts are paying 4.00%–5.00% APY. Varo Money tops the list at 5.00% (on balances up to $5,000 with qualifying direct deposit), while Axos Bank, SoFi, Valley Bank Direct, and others offer around 4.00%–4.21%. Any savings account paying less than 3.5% in the current environment is underperforming. Online banks consistently outperform traditional banks because they have lower overhead costs. Always confirm accounts are FDIC-insured (banks) or NCUA-insured (credit unions) up to $250,000.
APR (Annual Percentage Rate) is the simple, stated rate before compounding. APY (Annual Percentage Yield) is the effective annual rate after accounting for compounding — what you actually earn or pay over a full year. Savings accounts advertise APY (favorable — higher number shows real return). Loans advertise APR (which can understate the true cost if interest compounds frequently). The formula to convert: APY = (1 + APR/n)^n − 1, where n = compounding periods per year. A loan at 12% APR compounding monthly has an APY of 12.68%. Always compare products using the same metric — ideally APY — to get an apples-to-apples comparison.
More frequent compounding means interest is calculated and added to your balance more often, giving each new period a slightly higher base. On $10,000 at 5% for 10 years: annual compounding yields $16,289; monthly compounding yields $16,470; daily compounding yields $16,487. The difference between annual and daily is about $198 — modest at small amounts, but meaningful at scale. For a $500,000 retirement account at 7% over 30 years, switching from annual to monthly compounding adds approximately $178,000 to the final balance. This is why daily or monthly compounding savings accounts are always preferable to annual, all else equal.
The math is straightforward: if your debt's interest rate is higher than your savings account's APY, pay off the debt first. Credit card debt at 27.9% APR vs. a HYSA at 4% APY — paying off the card gives you a guaranteed 27.9% "return," which no savings account can match. However, there are nuances: keep at least 3–6 months of expenses in an emergency fund regardless; low-rate debt (mortgages below 4%, some student loans) may be worth carrying while investing surplus in assets expected to return more. Use our Loan Calculator to find your true borrowing cost, then compare to your savings rate using the Loan vs. Save mode above.
Use the Find Your Rate mode in our calculator. Enter your starting amount, ending amount (or total repaid for a loan), and the time period — the calculator solves for your implied annual rate using the compound interest formula in reverse. This is useful for evaluating whether a CD, savings bond, or investment is truly competitive, or for understanding what rate a lender effectively charged you when fees are included. For a loan, "ending amount" should be the total of all payments made, not just the final balance. For savings, it's your current account balance including all interest credited.
The Rule of 72 is a simple mental math shortcut to estimate how long it takes for money to double at a given compound interest rate. Divide 72 by the annual interest rate to get the approximate doubling time in years. For example: at 4% APY (a good HYSA rate in 2026), your money doubles in roughly 72 ÷ 4 = 18 years. At 8% (a reasonable long-term stock market return), it doubles in 9 years. At 27.9% (average credit card rate), a balance doubles in under 3 years if you're only making minimum payments. It's an excellent gut-check tool for quickly evaluating the power — or danger — of any interest rate.
Interest rates reflect risk, time, and competition. Lenders charge higher rates for riskier borrowers (lower credit scores), longer terms, and unsecured loans (no collateral). This is why credit cards charge 27.9% while mortgages charge 6.3% — a home serves as collateral, dramatically reducing lender risk. Savings accounts at big traditional banks pay 0.01%–0.60% because they don't need to compete aggressively for deposits; online banks with lower overhead pay 4%+ because deposits are their primary funding source. The Federal Reserve's benchmark rate sets the floor — banks borrow at the Fed rate and lend at a spread above it. When the Fed raises rates (as it did 2022–2023), both loan rates and savings rates rise. When it cuts (as in late 2024–2025), both tend to fall.
Yes. Interest earned on savings accounts, CDs, and money market accounts is fully taxable as ordinary income in the year it's credited, even if you don't withdraw it. Your bank will send you a Form 1099-INT if you earn $10 or more in interest during a calendar year. The interest is taxed at your marginal federal income tax rate (10%–37%) plus applicable state taxes. For a taxpayer in the 22% bracket earning 4% APY on $50,000, they'd owe approximately $440 in federal taxes on the $2,000 earned. Tax-advantaged accounts like HSAs, 529 plans, and certain IRAs offer exceptions — interest earned inside these accounts grows tax-deferred or tax-free depending on the account type.
The nominal interest rate is the stated rate before adjusting for inflation. The real interest rate is what you actually earn in purchasing power terms, calculated as: Real Rate ≈ Nominal Rate − Inflation Rate. If your HYSA pays 4.00% APY and inflation runs at 3.0%, your real return is approximately 1.0% — meaning your money grows, but only barely outpaces the rising cost of living. In 2022–2023, when inflation hit 8%+ while savings rates were near 0%, savers were earning deeply negative real returns — losing purchasing power even while their nominal balance grew. In 2026, with top HYSA rates at 4%+ and inflation around 3%, real returns are finally positive again for savers who choose the right accounts.