How does compound interest work in Kentucky?+
Compound interest works the same way in Kentucky as everywhere — the formula is A = P × (1 + r/n)^(n×t) + PMT × [((1 + r/n)^(n×t) − 1) / (r/n)], where P is principal, r is annual rate, n is compounding frequency, t is years, and PMT is regular contribution. What varies by state is the after-tax return on taxable accounts. In Kentucky, investment income (dividends, interest, short-term capital gains) is taxable at the 3.5% state rate, reducing the effective return on taxable accounts. At 7% gross, the state-tax-adjusted return is approximately 6.8% annually on ordinary income.
What does saving 10% of Kentucky's median income grow to over time?+
Kentucky's median household income is $64,526/year. Saving 10% ($6,453/year = $538/month) at 7% compounded monthly grows to: $93,120 after 10 years, $280,259 after 20 years, $656,344 after 30 years. Over 30 years, total contributions are $193,680 — but compound interest adds $462,664 more. That extra $462,664 is pure compound growth requiring no additional work.
What is the compound interest formula and how is it calculated?+
For a lump sum: A = P × (1 + r/n)^(n×t). For regular contributions: A = P × (1 + r/n)^(nt) + PMT × [((1 + r/n)^(nt) − 1) / (r/n)]. Monthly compounding (n=12) is the most common for savings accounts. Example: $10,000 in Kentucky at 7% monthly compounding for 30 years: A = $10,000 × (1 + 0.07/12)^(360) = $10,000 × (1.005833)^360 ≈ $81,165. The Rule of 72: divide 72 by the interest rate to estimate the doubling time. At 7%, money doubles in approximately 10.3 years.
Should I use a taxable account or tax-advantaged account in Kentucky?+
In Kentucky (3.5% income tax), tax-advantaged accounts (401(k), IRA, HSA) provide a compound advantage over taxable accounts. Every dollar in a Traditional 401(k) avoids both federal and 3.5% state income tax now. Every dollar in a Roth 401(k) grows tax-free and avoids state tax on withdrawals (subject to Partial pension exemption). In a taxable account, interest and short-term gains are taxed each year at your ordinary rate — compounding the drag on long-term growth.
What is the Rule of 72 and how does it apply to Kentucky investors?+
The Rule of 72 is a shortcut: divide 72 by your annual return rate to estimate how many years it takes for money to double. At 7%, money doubles in approximately 10.3 years. At 6%, about 12 years. At 4% (typical HYSA rate), about 18 years. For Kentucky investors in taxable accounts: if state income tax reduces your effective return from 7% to 6.8%, the doubling time extends from 10.3 years to approximately 10.6 years — a meaningful difference over a long investment horizon. This is one reason maximizing tax-advantaged accounts first is so valuable in higher-tax states.