Enter your initial deposit, interest rate, and time period. Choose compounding frequency and optionally add regular contributions. Toggle inflation adjustment to see real purchasing-power value.
| Year | Opening Balance | Contributions | Interest Earned | Closing Balance | Total Deposited |
|---|
See exactly how much more compound interest earns vs simple interest over the same period. The gap widens dramatically over longer timeframes — this is why compounding is called the "eighth wonder of the world."
Find the annualised growth rate of any investment. CAGR tells you what constant annual rate would produce the same result as the actual (possibly uneven) growth. Essential for comparing investments over different periods.
The Rule of 72 estimates how long it takes to double your money. Divide 72 by your annual rate. Works in reverse too — enter how many years you want to double in and find the required rate. We show both the quick estimate and the mathematically exact answer. Want the full explanation? Read our Rule of 72 guide for formula walkthroughs, doubling charts, and how fees affect your results.
| Annual Rate | Rule of 72 (approx) | Exact Years | Benchmark |
|---|---|---|---|
| 2% | 36.0 yrs | 35.0 yrs | Base inflation |
| 3% | 24.0 yrs | 23.4 yrs | Target inflation |
| 4% | 18.0 yrs | 17.7 yrs | Conservative savings |
| 5% | 14.4 yrs | 14.2 yrs | HYSA / CDs 2026 |
| 6% | 12.0 yrs | 11.9 yrs | Balanced portfolio |
| 7% | 10.3 yrs | 10.2 yrs | S&P 500 real return |
| 8% | 9.0 yrs | 9.0 yrs | Growth portfolio |
| 10% | 7.2 yrs | 7.3 yrs | S&P 500 nominal avg |
| 12% | 6.0 yrs | 6.1 yrs | Higher-risk target |
Work backwards from a target amount. Enter your goal, timeline, rate, and initial savings — we calculate the exact monthly contribution needed to reach it. Great for retirement, house down payment, college fund, or any financial goal.
Compound Interest Explained — Formula, Frequency, CAGR & the Rule of 72
Compound interest is one of the most powerful forces in personal finance. Here's how it works, why frequency matters (less than you think), and the key numbers for 2026 planning.
The Core Formula
A = P × (1 + r/n)^(n×t)
Where: P = Principal · r = Annual rate (decimal) · n = Compounding periods per year · t = Years
With regular contributions (monthly PMT):
A = P × (1+r/n)^(n×t) + PMT × [((1+r/n)^(n×t) − 1) ÷ (r/n)]
Example: $10,000 at 7%, monthly compounding, 20 years = $40,552. With $300/month added: $194,683. The contributions multiplied the result nearly 5×.
Does Compounding Frequency Matter Much?
At 5% APR on $10,000 over 10 years: Annual → $16,289 · Monthly → $16,470 · Daily → $16,487. The difference between annual and daily compounding is only $198 over a decade. Frequency matters far less than the rate and how long you stay invested. Always compare accounts using APY (not APR) — it already accounts for compounding frequency and puts everything on equal footing.
Typical 2026 Rates by Asset Class
| Asset / Account | Typical Rate (2026) | Risk Level |
|---|---|---|
| High-Yield Savings Account (HYSA) | 4.0–5.0% APY | None (FDIC insured) |
| Certificate of Deposit (5-year) | 4.25–5.25% APY | None (FDIC insured, locked-in) |
| Investment-Grade Bonds | 3.5–5.0% | Low |
| Balanced Portfolio (60/40) | 5–7% avg | Moderate |
| S&P 500 Index Fund (nominal) | ~10% historical avg | High (volatile year-to-year) |
| S&P 500 Index Fund (real, after inflation) | ~7% historical avg | High |
The Rule of 72 — Quick Reference
Divide 72 by your annual rate to estimate doubling time: at 6%, your money doubles in 12 years; at 8%, in 9 years; at 10%, in 7.2 years. It also works for inflation: at 3% CPI, purchasing power halves in 24 years. Most accurate for rates between 4–12%. For precision, use the exact formula: Years = ln(2) ÷ ln(1 + r).
APR vs APY — Always Compare APY
APR is the stated rate. APY = (1 + APR/n)^n − 1 accounts for compounding. A 5% APR compounded monthly is 5.116% APY; daily is 5.127% APY. Banks are required to disclose APY on savings products. Always compare savings accounts using APY to get a fair comparison regardless of how often each account compounds.