What is compound interest and why does it matter?

$10,000 at 8% with monthly compounding grows to $22,196 in 10 years — not $18,000 as with simple interest. The extra $4,196 is pure compounding. Starting 10 years earlier roughly doubles your ending balance. Use the Compound Interest Calculator above to model any scenario.

What is a good ROI on an investment?

The S&P 500 has averaged approximately 10% annually since 1957 (7% real). Any annualized return consistently above 15% is considered excellent. Use the ROI Calculator to benchmark your actual returns.

How much do investment fees cost over time?

A 1% annual fee on a $100,000 portfolio at 8% over 30 years costs approximately $198,000 in lost wealth — nearly 20% of your final balance. Low-cost index funds at 0.03% cost virtually nothing by comparison. The Fee Impact Calculator shows your exact cost.

What is Dollar Cost Averaging (DCA)?

DCA means investing a fixed amount at regular intervals regardless of price. When prices fall you buy more shares; when they rise you buy fewer. Research shows DCA reduces the risk of investing a lump sum at a market peak. Use the DCA Calculator to model your specific scenario.

How do I calculate stock profit?

Net profit = (sell price - buy price) x shares - all commissions. ROI = net profit divided by total buy cost. Break-even sell price = (total buy cost + sell commission) divided by shares. Use the Stock Profit Calculator for instant results including break-even price.

What is dividend yield?

Dividend yield = annual dividend per share divided by stock price, expressed as a percentage. A $2 annual dividend on a $50 stock = 4% yield. The S&P 500 averages around 1.5%. Yields of 3-5% are considered high-yield. Use the Dividend Yield Calculator for income projections.

How does inflation affect investment returns?

A 7% nominal return with 3% inflation gives only 3.88% real return. Over 20 years, $10,000 grows to $38,697 nominally but only $21,911 in today's purchasing power. Use the Inflation-Adjusted Return Calculator to see both figures side by side.

How long does it take to double my money?

Use the Rule of 72: divide 72 by your annual return. At 8%, money doubles in 9 years. At 10%, 7.2 years. At 6%, 12 years. The Compound Interest Calculator gives the exact figure for any rate and contribution amount.

What is a good portfolio allocation?

A common rule is 110 minus your age in stocks. At 30, that's 80% stocks, 20% bonds. The classic 60/40 portfolio has returned ~8% historically with lower volatility than all-stocks. Rebalance annually or when any asset drifts more than 5% from target.

How are crypto profits taxed in the US?

Crypto is taxed as property. Short-term gains (under 12 months) are taxed as ordinary income up to 37%. Long-term gains are taxed at 0%, 15%, or 20% depending on income. The wash sale rule does not apply to crypto. Always consult a tax professional.

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Not sure which return rate to use in the calculators above? The table below shows what the S&P 500 has actually returned — decade by decade, in real numbers.

Reference Data

S&P 500 Average Annual Return by Decade (1950–2024)

Real annualized S&P 500 returns for each decade since 1950 — total return including dividends reinvested. Use these as the benchmark rate in the calculators above. Reference Data · Q1 2025

Annualized S&P 500 Return by Decade (nominal, price + dividends)

+19.4%

+7.8%

+5.9%

+17.5%

+18.2%

−0.95%

+13.6%

+14.5%

1950s

1960s

1970s

1980s

1990s

2000s

2010s

2020s*

Decade	Annualized Return	Best Single Year	Worst Single Year	$10k grew to
1950s	+19.4%	1954: +52.6%	1957: −10.5%	~$57,000
1960s	+7.8%	1961: +26.9%	1966: −10.1%	~$21,000
1970s	+5.9%	1975: +37.2%	1974: −26.5%	~$17,700
1980s	+17.5%	1985: +31.6%	1981: −4.9%	~$48,700
1990s	+18.2%	1995: +37.6%	1990: −3.1%	~$53,000
2000s	−0.95%	2003: +28.7%	2008: −37.0%	~$9,100
2010s	+13.6%	2013: +32.4%	2018: −4.4%	~$35,900
2020s *	+14.5%	2021: +28.7%	2022: −18.1%	In progress
Long-run avg 1950–2024	~10.1%	All-time best: 1954 +52.6%	All-time worst: 1931 −43.8%	~7% real

* 2020s data through end of 2024 only (5 years). Returns include dividends reinvested (total return). Reference Data · Q1 2025. Source: Standard & Poor's, Yale/Shiller data. Past performance does not guarantee future results.

−43.8%

Worst single year
(1931)

Why DCA matters

What the Data Tells Us

Time in market beats timing

Despite the 2000s "lost decade," a continuous investor from 1990 to 2024 averaged over 10% annually. Missing just the 10 best days per decade cuts returns by more than half.

Lost decades do happen

The 2000s produced a −0.95% annualized return — two major crashes (dot-com and financial crisis) wiped out an entire decade of gains. Asset allocation and DCA protect against this.

Dividends are ~40% of returns

Price-only S&P 500 returns average ~6.5%. Total return (including reinvested dividends) averages ~10.1%. Dividends account for nearly 40% of long-run equity returns.

Use these returns in the calculators above

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12 free investing guides — the context and frameworks behind every calculator on this site. Use the tools above to run the numbers; use these to understand what the numbers mean.

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Investing Basics

How Compound Interest Works

Discover why starting early matters more than earning more — and how to model any growth scenario with the compounding formula.

Total ROI, annualized return, and why the formula you use changes the answer — including which version every investor should know.

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Investing Basics