Our free compound interest calculator covers every financial scenario — from savings growth to loan costs. Click any card to load that mode.
Our compounding interest calculator shows how interest compounds on interest over time. The most powerful concept in personal finance — use daily, monthly, quarterly, or annual frequency.
Calculate how much interest your savings account will earn. Works as an interest calculator savings and savings interest calculator — includes monthly deposits.
Calculate APY, maturity amount, and interest earned on CDs. Our CD interest calculator shows effective yield and exact payout at term end.
Our loan interest calculator, mortgage interest calculator, and car loan interest calculator all use the same amortization formula — with full payment table.
Our free interest calculator is more complete than calculator.net, the investor.gov compound interest calculator, and the Elementor interest calculator — because it covers 6 different modes in one tool: compound interest calculator, simple interest calculator, loan interest calculator, credit card interest calculator, CD interest calculator, and savings account interest calculator. Each mode provides the right formula, the right inputs, and a full year-by-year breakdown. Our compounding interest calculator also supports daily, monthly, quarterly, semi-annual, and annual compounding — matching the precision of the NerdWallet compound interest calculator.
The compound interest calculator uses: A = P(1 + r/n)^(nt). Where A = final amount, P = principal, r = annual rate (decimal), n = compounding frequency per year, t = time in years. Interest earned = A − P.
$10,000 at 6% for 10 years, compounded monthly:
n = 12 · r = 0.06 · t = 10
A = $10,000 × (1 + 0.06/12)^(12×10)
A = $10,000 × (1.005)^120 = $10,000 × 1.8194
A = $18,194 · Interest Earned = $8,194
Compare: Simple interest on same = $10,000 × 6% × 10 = $6,000 only — compound earns $2,194 more!
The simple interest calculator formula: I = P × r × t. Simple interest is calculated only on the original principal — no interest on interest. It grows linearly. The compound interest calculator calculates interest on principal PLUS accumulated interest — it grows exponentially. For borrowers: simple interest loans (some car loans) cost less than compound interest loans. For savers: compound interest savings accounts grow faster than simple interest accounts. Always prefer compound interest when saving; prefer simple interest when borrowing.
The credit card interest calculator reveals why credit card debt is so dangerous. Credit cards use daily compounding (n=365) with very high APRs (typically 20–29%). Monthly interest = Balance × APR/12. On a $5,000 balance at 24% APR: monthly interest = $100. If you only pay the $25 minimum, almost all of it goes to interest and fees — your balance barely moves. Use our credit card interest calculator mode to see exactly how much your balance costs each month and how long it takes to pay off at different payment levels.
Credit card warning: A $5,000 balance at 24% APR paying only the minimum takes over 20 years to pay off and costs more than $7,000 in interest alone — paying back nearly $12,000 total on a $5,000 balance. Our credit card interest calculator shows this total cost so you can make an informed decision about debt payoff strategy.
Our loan interest calculator uses the amortization formula: PMT = P × r(1+r)^n / ((1+r)^n − 1). This works for any installment loan — use it as a car interest calculator / car loan interest calculator, mortgage interest calculator, or personal loan interest calculator. Total interest = (Monthly Payment × Total Months) − Principal. The amortization table shows how much of each payment goes to principal vs interest — early payments are mostly interest, later payments mostly principal.
| Loan Type | Example Amount | Rate | Term | Monthly Payment | Total Interest |
|---|---|---|---|---|---|
| Car Loan | $25,000 | 7% | 60 mo | $495 | $4,702 |
| Mortgage | $350,000 | 7% | 30 yr | $2,329 | $488,560 |
| Personal Loan | $15,000 | 12% | 48 mo | $394 | $3,922 |
| Student Loan | $40,000 | 6% | 120 mo | $444 | $13,280 |
CDs (Certificates of Deposit) and high-yield savings accounts (HYSA) use compound interest to grow your money. Our CD interest calculator shows the exact payout at maturity based on deposit amount, APY, and term length. Current 1-year CD rates (2024) range from 4.5–5.5% APY. Our savings account interest calculator / savings interest calculator adds monthly deposits to model ongoing savings growth — essential for emergency fund planning and short-term goals.
The daily compound interest calculator uses n=365 in the compound formula. Most US savings accounts and credit cards compound daily, even if they pay interest monthly. The difference between daily and monthly compounding is small on a single year but meaningful over decades. For a $100,000 savings account at 5% for 20 years: monthly compounding = $271,264; daily compounding = $271,828 — a $564 difference. Our daily interest calculator and monthly interest calculator modes let you compare these side-by-side.
The monthly compound interest calculator shows why banks advertise APY (Annual Percentage Yield) rather than APR. APY accounts for monthly compounding's boost. Relationship: APY = (1 + APR/12)^12 − 1. At 5% APR compounded monthly: APY = (1 + 0.05/12)^12 − 1 = 5.116%. That 0.116% difference adds up significantly on large balances over long periods.
Rule of 72 for compound interest: Divide 72 by your interest rate to estimate how long it takes your money to double. At 5% (daily compound): 72 ÷ 5 = 14.4 years to double. At 8%: 72 ÷ 8 = 9 years. At 10%: 72 ÷ 10 = 7.2 years. This works for any compounding frequency. Use our compounding interest calculator to verify the exact doubling time for any rate.
Questions covering compound interest formula, simple vs compound, credit card interest, CD calculator, loan interest, savings account, daily compounding, and more.
The compound interest formula: A = P(1 + r/n)^(nt). Where A = final amount, P = principal (starting amount), r = annual interest rate as decimal (5% = 0.05), n = number of times interest compounds per year (daily=365, monthly=12, quarterly=4, annually=1), t = time in years. Interest = A − P. Example: $5,000 at 6% compounded monthly for 3 years: A = $5,000 × (1 + 0.06/12)^(12×3) = $5,000 × 1.1967 = $5,983.40. Interest earned = $983.40. Use our compounding interest calculator to compute any scenario instantly.
Simple interest formula: I = P × r × t. Calculated only on original principal — grows linearly. Compound interest: interest is earned on principal PLUS previously accumulated interest — grows exponentially. Example comparison ($10,000 at 8% for 20 years): Simple interest: $10,000 + ($10,000 × 8% × 20) = $26,000. Compound (monthly): $10,000 × (1 + 0.08/12)^240 = $49,268 — nearly double! Our simple interest calculator and compound interest calculator show both results so you can see the difference on your specific numbers.
Credit cards use daily compounding. Daily periodic rate = APR ÷ 365. Average daily balance × daily rate × days in billing cycle = monthly interest charge. Example: $3,000 balance at 21% APR: Monthly interest = $3,000 × (21% ÷ 12) = $52.50/month. If you pay only the minimum (~$60), only $7.50 reduces the principal. At this rate it takes years and thousands in interest to pay off. Our credit card interest calculator mode shows total interest paid over different payoff timelines and minimum-vs-fixed-payment comparisons.
CDs use the compound interest formula with a fixed rate and term. Most CDs compound daily. Our CD interest calculator: enter your deposit amount, APY (annual percentage yield), and term. Example: $20,000 CD at 5.0% APY for 18 months: A = $20,000 × (1 + 0.05/365)^(365×1.5) = $20,000 × 1.0779 = $21,557. Interest earned = $1,557. Always use APY (not APR) for CDs — APY accounts for compounding, giving you the true annual return. Select "CD / Fixed Deposit" mode in our interest calculator above.
Our car loan interest calculator, car interest calculator, and mortgage interest calculator all use the loan amortization formula: Monthly Payment = P × r(1+r)^n ÷ ((1+r)^n − 1). Example car loan: $30,000 at 7% for 60 months: Monthly = $594. Total paid = $35,640. Total interest = $5,640. Mortgage example: $400,000 at 7% for 30 years: Monthly = $2,661. Total paid = $958,000. Interest = $558,000. Use "Loan / Mortgage" mode in our loan interest calculator and see the full amortization table showing principal vs interest breakdown for every payment.
The daily compound interest calculator formula: A = P × (1 + r/365)^(365×t). This is the most precise compounding — used by banks for savings accounts, HYSAs, and credit cards. Example: $50,000 at 4.5% daily compound for 5 years: A = $50,000 × (1 + 0.045/365)^(365×5) = $50,000 × 1.2523 = $62,615. Interest = $12,615. Vs annual compounding: $62,312 — daily earns $303 more over 5 years. Our daily interest calculator and daily compound interest calculator show the exact difference for any scenario.