Compound Interest Calculator Project investment growth, compare compounding frequencies, and model real returns — with 20...

Compound Interest Calculator

Project investment growth, compare compounding frequencies, and model real returns — with 2025 benchmarks and visual analytics.

Lump Sum

Regular Contributions

Compounding Frequency

Inflation-Adjusted

Initial Investment ($)

Annual Return (%)

Years

Compounding Annual Quarterly Monthly Daily Continuous

Initial Investment ($)

Monthly Contribution ($)

Years

Annual Return (%)

Principal ($)

Rate (%)

Years

Nominal FV ($)

Inflation Rate (%)

Years

$0

Future Value

$0

Interest Earned

0.00%

Effective Annual Rate

$0

Inflation-Adjusted

Growth Over Time

Compound Interest Formulas

Lump Sum**:

$$FV = P \left(1 + \frac{r}{n}\right)^{nt}$$

Continuous Compounding**:

$$FV = Pe^{rt}$$

Regular Contributions (Annuity)**:

$$FV = PMT \times \frac{(1 + r)^t - 1}{r}$$

Example** ($10K @ 7%, 30 yrs): • Annual: $10,000 × (1.07)³⁰ = **$76,123** • Monthly: $10,000 × (1 + 0.07/12)³⁶⁰ = **$81,165** • Continuous: $10,000 × e^2.1 = **$81,662**

✅ Pro Tip**: The difference between daily and continuous is negligible for most practical purposes.

Compound Interest Red Flags

⚠️ Avoid these common pitfalls:

• Nominal vs. effective rate confusion** — 7% APR compounded monthly = 7.23% EAR
• Ignoring fees** — 1% AUM fee = −1% to net return → $214K less on $500/mo/30yrs
• Teaser APYs** — 5.25% “for 6 months” → 0.50% after
• Using simple interest formulas** — underestimates growth significantly over time

✅ Smart Investor Tips**:

• Compare accounts by **APY (Annual Percentage Yield)**, not APR
• Reinvest dividends/interest — let compounding work fully
• Start early: $200/mo at 25 → 65 = $651K; same at 35 = $520K

2025 Compound Interest Benchmarks

Compounding	$10K @ 7% (30 yrs)	Effective APR
Annual	$76,123	7.00%
Quarterly	$79,178	7.19%
Monthly	$81,165	7.23%
Daily	$81,648	7.25%
Continuous	$81,662	7.25%

📉 Rule of 72**: 7% return → doubles in **10.3 years** 📉 Volatility Drag**: 15% std dev reduces CAGR by ~1.1%

How to Use This Calculator

➡️ Lump Sum

“$10K invested today @ 7% for 30 yrs → what’s it worth?” (Answer: $81,165 monthly comp.)

➡️ Regular Contributions

“$500/mo for 30 yrs @ 7% → how much will I have?” ($566,765)

➡️ Compounding Frequency

Compare annual vs. daily — see how frequency impacts long-term growth.

➡️ Inflation-Adjusted

“$81,662 nominal → what’s the real value after 3% inflation for 30 yrs?” ($33,400)

Note: Uses exact compound formulas. EAR = (1 + r/n)ⁿ − 1. Inflation adjustment: FV ÷ (1 + π)^t.