Compound Interest Calculator

About $100,627 with annual compounding, or $109,357 with daily compounding. The same $10,000 in a 4% HYSA would grow to about $32,434 over 30 years. Stocks (historical 8–10% nominal return) compound dramatically more than savings accounts over decades.

APR is the simple annual rate; APY includes compounding within the year. A 5% APR compounded daily becomes a 5.127% APY. Truth in Savings Act (Regulation DD) requires US banks to disclose APY on deposit accounts so you can compare apples to apples.

Divide 72 by your annual return rate to estimate years to double your money. At 8% return, money doubles in roughly 9 years (72/8). At 4% return, it doubles in 18 years. The shortcut is most accurate for rates between 5% and 12%; outside that range it overestimates slightly.

It depends on your timeline. CFPB and most personal finance guidance recommend cash savings (HYSA) for goals within 3 years and emergency funds, while index-fund investing (S&P 500, total market) is appropriate for goals 5+ years away. Stocks carry short-term volatility but historically earn 8–10% nominal returns long-term vs. 4–5% for HYSAs.

Starting at age 25 with 30 years until age 55: about $610/month at 8% annual return. Starting at 35 with 25 years: about $1,047/month. Starting at 45 with 15 years: about $2,891/month. Starting earlier is exponentially more powerful — the compound interest formula rewards time more than monthly amount.

Yes — interest from HYSAs, CDs, and money market funds is taxed as ordinary income at your federal marginal tax rate plus state income tax (where applicable). Banks send a 1099-INT for interest above $10. Tax-advantaged accounts (Roth IRA, traditional IRA, 401(k), HSA, 529) shelter compound growth from these taxes.

Less than you'd think. On a 5% rate, the difference between annual and daily compounding over 30 years is about 4% of the ending balance — meaningful but small. The vastly bigger drivers are rate (5% vs 8%) and time (20 vs 30 years). Don't pick a low-rate account for slightly more frequent compounding.

HYSA APY tends to follow the Federal Funds rate within 1–2 months. When the Fed cuts rates, banks lower deposit rates within weeks. CDs lock in a rate at purchase, so they protect against future cuts — useful in a falling-rate environment if you don't need liquidity. Lock in CDs when the Fed signals coming cuts; keep cash in HYSAs when rates are rising.