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.
A savings projection combines a starting balance with regular deposits and compound growth, and its most useful output is not the final number but the split between what you put in and what the interest added. Early in any savings plan, contributions dominate almost entirely — growth is a rounding error on a small balance. The crossover, where annual growth begins to exceed annual contributions, is the point at which the account starts doing more work than the saver, and identifying when it arrives is far more motivating than any single projected total.
FV = P(1 + r)^n + PMT × [ ((1 + r)^n − 1) ÷ r ]Total contributed = P + (PMT × n)Growth = FV − Total contributedCrossover: when balance × r > PMTwhere:
Assumptions: Assumes a constant rate and deposits made at period end. Savings interest is taxable as it is earned in a taxable account, which reduces the balance available to compound.
Ten years of steady saving, split into contributions and growth, with the crossover identified.
Result$48,493 after ten years — $10,493 of it interest
The crossover point here arrives when the balance reaches $300 ÷ 0.00375 = $80,000, which is past year ten. That is characteristic of cash savings: at 4.5% the account only starts out-earning the saver after many years, whereas at an equity-like 8% the crossover comes far sooner.