Investing 101: Stocks, Bonds, and Understanding Risk

Picking funds is the easy part of investing. Learn stocks, bonds, index funds, risk and goal-setting, and write the plan that keeps you invested.

By Michael Hewitt, Founder & Editor-in-Chief. Updated September 28, 2026.

Most beginners think the hard part of investing is choosing what to buy. It is the easy part: three index funds cover the whole market for under 0.10% a year. The hard part is behavior. DALBAR's annual study of fund flows has found, year after year, that the average stock fund investor earns less than the funds they own, because money arrives after prices have risen and leaves after they have fallen. Stocks, bonds and funds take an afternoon to understand. Sitting still through a bad year is the skill that pays, and the way to manage it is a plan written before the bad year arrives.

The Three Core Asset Classes

Everything you can invest in is a slice of a business, a loan, or cash. The trade between them is simple: more expected return costs more short-term pain.

• Stocks (equities): ownership in companies. The highest long-run return, and single years for the S&P 500 have ranged from -43% to +54%.
• Bonds (fixed income): loans to governments or companies. Lower return, much smaller swings.
• Cash and equivalents: savings, money market funds, T-bills, short-term CDs. The lowest return and no real risk to principal.

Stocks: What You Own

A share is a small claim on a real company's profits, assets and growth. Its price is the market's estimate of future earnings, discounted to today. Over the long run, prices track earnings growth plus dividends.

• S&P 500: the 500 largest U.S. companies, about 80% of U.S. stock market value, and the usual benchmark.
• Total Stock Market (VTI, FSKAX): about 4,000 U.S. companies, adding mid and small caps.
• International (VXUS, IXUS): Europe, Japan, Australia, Canada and emerging markets, about 40% of global market value.
• Emerging markets on their own (VWO): China, India, Brazil, Taiwan. More growth potential, more political and currency risk.

Bonds: Lending Money for Fixed Payments

A bond is a loan. You hand a government or company money, it pays you interest (the coupon) and returns the principal at maturity. The job of bonds in a portfolio is shock absorption when stocks fall.

• U.S. Treasuries: backed by the federal government and treated as free of default risk. Terms run from 2 to 30 years.
• Corporate bonds: higher yields than Treasuries in exchange for credit risk. Investment grade is BBB and above; high-yield (junk) is BB and below.
• Municipal bonds: issued by states and cities, with interest free of federal tax and often state tax. Most useful to high earners in taxable accounts.
• The price rule: when interest rates rise, existing bond prices fall, and the longer the bond, the bigger the drop.

Cash Equivalents: The Role of Safety

HYSAs, money market funds, T-bills and short-term CDs protect principal and earn the risk-free rate. Cash has three jobs: the emergency fund, goals due within 1-3 years, and dry powder for buying during a crash. Cash beyond those three jobs is a drag on long-term wealth.

Funds: Diversification in One Purchase

A fund holds hundreds or thousands of stocks or bonds, so one purchase buys the diversification you could never assemble share by share. Two kinds matter:

• Index funds: track a market index such as the S&P 500, with fees of 0.03-0.20% and no manager trying to beat the market.
• ETFs (exchange-traded funds): trade like stocks, usually track an index, and typically have lower minimums than mutual funds.

Why Index Funds Beat Active Management

S&P Global's SPIVA Scorecard counts how many active funds trail their benchmark after fees. In its year-end 2025 edition, about 90% of large-cap U.S. funds trailed the S&P 500 over 15 years, which puts the odds of picking a winner in advance at roughly 1 in 10. The record gets worse the longer you look:

• 1 year: 79% of large-cap funds lost to the S&P 500 in 2025, and 65% in 2024.
• 15 years: about 90% lost.
• The arithmetic behind it: if the market returns 10% and a fund charges 1%, the manager has to beat the market by a full point every year just to tie the index.

The Only Funds Most People Need

Two or three funds give you a globally diversified portfolio. The three-fund portfolio popularized by the Bogleheads captures nearly all available diversification at close to the lowest possible cost. Complexity is not a feature.

• Fund 1: U.S. Total Stock Market (VTI at 0.03% or FSKAX at 0.015%), about 4,000 U.S. companies.
• Fund 2: International Total Stock (VXUS or FTIHX, both under 0.10%), about 8,000 non-U.S. companies.
• Fund 3: U.S. Total Bond Market (BND at 0.03% or FXNAX at 0.025%), about 10,000 investment-grade bonds.
• A starting mix for a 30-year-old: 60% U.S. stock, 30% international stock, 10% bonds, moving toward bonds as retirement approaches.
• Or one target-date fund (Vanguard Target Retirement 2060, VTTSX, for example), which holds the mix and rebalances it for you.

ETF vs Mutual Fund: Which Format

Both hold the same securities, so the choice is mechanical. ETFs trade during the day, have no minimums and are slightly more tax-efficient in taxable accounts. Mutual funds make automatic dollar-amount investing simpler, which suits recurring contributions.

• Taxable brokerage account: use ETFs, for the tax efficiency and because they are commission-free at every major broker.
• 401(k) and IRA: use mutual funds, for automatic investing without thinking about bid/ask spreads.
• Performance difference: none. VTI and VTSAX hold the same stocks and return the same, apart from minor tax differences.

Compounding: What a Late Start Costs

Compounding is growth on growth, and it is back-loaded: it does little for a decade and most of its work at the end. $10,000 at a 7% real return becomes $19,672 in 10 years, $38,697 in 20 and $76,123 in 30. The first decade adds about $10,000. The third adds about $37,000 on its own, with nothing new put in.

• $300 a month from age 25 to 65 at 7%: about $787,000.
• $300 a month from age 35 to 65 at 7%: about $367,000.
• The Rule of 72: divide 72 by the annual return to get the years it takes to double. At 7%, about 10.

Dollar-Cost Averaging: Compounding's Partner

Dollar-cost averaging means investing a fixed amount on a fixed schedule whatever the price. High prices buy fewer shares and low prices buy more, so your average cost per share ends up below the average price, and the question of when to buy disappears.

• Example: $500 a month into VTI. January at $250 buys 2 shares, February at $230 buys 2.17, March at $260 buys 1.92.
• Average cost: $246.02 a share, against an average market price of $246.67.
• Lump sum vs DCA: in Vanguard's research, investing a lump sum at once beat spreading it out about two-thirds of the time, because markets tend to rise. DCA wins on consistency, and the plan you stick to beats the one you abandon.
• Automate it: recurring purchases on the 1st and 15th, or on payday, and market timing stops being a decision.

Nominal vs Real Returns: What You Keep After Inflation

The 10% stock return quoted everywhere is nominal. What your money will buy grew by about 3 points a year less. Every asset looks different once inflation comes out:

• S&P 500, 1928-2024: 10.1% nominal, 7.0% real.
• Bonds (10-year Treasury), 1928-2024: 4.9% nominal, 1.9% real.
• Cash (T-bills), 1928-2024: 3.3% nominal, 0.3% real. Cash barely beats inflation.
• Gold, 1928-2024: 4.6% nominal, 1.6% real, and worse than stocks over every long window.

SMART Goals: Set the Target in Today's Dollars

"Invest more" is not a plan. A goal you can act on has a number and a date ("$1.2 million across my 401(k) and IRA by 65"), which is most of what the SMART framework (specific, measurable, achievable, relevant, time-bound) asks for. Work backward from the number to a monthly contribution, then check progress once a year on a date you will not forget, such as a birthday or tax day.

The catch is the unit the number is written in. At 2.5% inflation, $1 million in 2056 buys roughly what $500,000 buys today. A goal stated in future dollars has to be about twice the size of the same goal in today's dollars, and a goal in today's dollars has to be projected with the real return from the table above, not the nominal one.

• The goal: $1.2 million of today's buying power in 2056, 30 years out. In 2056 dollars, at 2.5% inflation, that is about $2.5 million.
• The mistake: write the target as "$1.2 million" and project it at a 10% nominal return. The plan asks for about $530 a month, and in 2056 the $1.2 million buys what about $570,000 buys today, less than half the goal.
• The fix: keep the target in today's dollars and project it at 7% real. $820 a month builds $1 million in 30 years, so $1.2 million takes about $985 a month, raised each year by inflation. The real-return math assumes you make that raise.
• The limit check: $985 a month is more than an IRA will take ($7,500 in 2026, or $625 a month), so the plan needs a 401(k) or a taxable account alongside it.
• Other targets at 7% real: $100,000 in 10 years takes about $580 a month, $500,000 in 20 years about $960, and $1 million in 25 years about $1,235.

Risk Depends on When You Need the Money

Risk is not whether you can lose money. It is how likely a loss is, and how large, over the time you have, and the horizon changes those odds more than anything else you control.

Short-term volatility is the price of long-term returns. Anyone offering stock-like returns without it is selling something.

Risk by Time Horizon

• 1 year: stocks lose money in about 25% of years. The worst single year was -43% (1931).
• 5 years: stocks lose money in about 12% of rolling 5-year periods. The worst was -12.5% a year (1928-1932).
• 10 years: stocks lose money in about 5% of rolling 10-year periods. The worst in recent memory was 1999-2008, about -1.4% a year before inflation.
• 20 years: no rolling 20-year period since 1926 has lost money after inflation.
• What to do with it: money you need within 5 years belongs in bonds or cash. Money you will not touch for 20 years can be almost entirely stocks.

The Risks That Do Not Show Up on a Chart

Volatility gets the attention, but the costs that do the most damage come from what investors do, or fail to do.

• Inflation: cash earning 0.01% loses 3% or more of its buying power a year. Over 30 years, $100,000 becomes about $41,000 in real terms. For long-term money, not investing is the larger risk.
• Behavior: the gap between what funds return and what their investors earn comes from selling in drops and buying after rallies, and it can cost more than any fee below.
• Fees: 1% a year on a $500,000 portfolio is $5,000 a year, whatever the market does. The fee section below does the long-run math.

Sequence of Returns: Why Order Matters

Two investors with the same average return over 30 years can end with very different balances if the good and bad years arrive in a different order. It matters most in the 5 years either side of retirement.

• While you are contributing, bad years early help: you buy more shares cheaply and the recovery compounds for decades.
• While you are withdrawing, bad years early hurt most: you sell shares at low prices and those shares are gone for good.
• Example: after a 30% drop in the first year of retirement, the same withdrawal requires selling 43% more shares.
• Protection: move 5-10% of the portfolio from stocks to bonds or cash in the 5 years before retirement (the "bond tent").

Key Takeaways

• Picking funds is the easy part; the average fund investor trails the funds they own by buying after rallies and selling in drops, so the plan matters more than the pick.
• Three index funds costing under 0.10% a year cover the whole market, while about 90% of large-cap active funds trailed the S&P 500 over 15 years.
• Set goals in today's dollars and project them at a 6-7% real return, because at 2.5% inflation $1 million in 2056 buys roughly what $500,000 buys today.
• Money you need within five years belongs in bonds or cash; money you will not touch for 20 years can be almost all stocks.