Calculate how much your savings will grow over time with compound interest. See your final balance, total interest earned, and year-by-year growth for any savings account, high-yield savings, or investment account. Includes monthly contribution modeling. Free, instant, no sign-up.
Compound interest with monthly contributions
Compound interest is often called the eighth wonder of the world — and for good reason. When interest is added to your principal and then earns interest itself, the growth becomes exponential rather than linear. A one-time deposit of $10,000 at 4.5% APY grows to $15,530 in 10 years, $24,117 in 20 years, and $37,453 in 30 years — without adding another dollar. Add $300/month contributions and those same numbers become $59,386 at 10 years, $145,888 at 20 years, and $283,673 at 30 years. The math clearly rewards two behaviors: starting early and adding consistently.
In 2026, high-yield savings accounts (HYSAs) are offering 4.5–5.1% APY at online banks like Marcus, Ally, and SoFi — dramatically higher than the 0.06% national average at traditional brick-and-mortar banks. FDIC insurance covers up to $250,000 per depositor per institution. For emergency funds (the recommended 3–6 months of expenses) and short-term savings goals (1–5 years), HYSAs are the optimal savings vehicle. For longer time horizons (5+ years), index funds in a Roth IRA or taxable brokerage account typically outperform HYSAs significantly, though with more volatility. Always match your savings vehicle to your time horizon and risk tolerance.
High-yield savings: 4.5–5.1% APY. Money market accounts: 4.0–4.8%. 12-month CDs: 4.5–5.0%. 5-year CDs: 4.0–4.5%. Traditional bank savings: 0.01–0.06%. Switching to a HYSA from a traditional account can earn 70x more interest on the same balance.
Before investing, build 3–6 months of living expenses in an FDIC-insured HYSA. This is the financial cushion that prevents you from cashing out investments during a job loss or emergency. Once funded, invest the rest in tax-advantaged accounts (Roth IRA, 401k) before taxable brokerage.
Daily compounding earns slightly more than monthly, which earns more than annual. On $50,000 at 5% for 10 years: annual compounding = $81,445 vs daily compounding = $82,436 — a $991 difference. For most savings accounts, the effect is small but compounds over longer periods.
Divide 72 by your interest rate to estimate doubling time. At 4.5% APY: 72/4.5 = 16 years to double. At 7% (stock market avg): 72/7 = ~10 years. At 10%: 72/10 = 7.2 years. Use this mental shortcut to quickly evaluate if a savings account rate is worthwhile for your goal timeline.