Money Foundations · 10 min read
Stocks, Bonds, and the Funds That Hold Them
ETFs, mutual funds, index funds, expense ratios — the four-word vocabulary lesson medical school skipped, and the fee math that pays for a house.
Reviewed by Jonathan Shafer, DO, July 2026. Disclosure: the reviewer is the founder and owner of Attending Financial LLC. This is education, not individualized financial advice.
The vocabulary nobody taught you
You can graduate medical school, finish residency, and sign a $350,000 contract without anyone ever telling you what an ETF is. Then a enrollment form lands with thirty fund names on it and you pick whatever sounds prudent. The entire subject rests on four words — stock, bond, fund, index — and one number, the expense ratio. Ten minutes here covers what they are and the six-figure difference the last one makes.
The building blocks
Tap each card. Everything in your retirement account is assembled from these.
Stock
A share of ownership in one company. You participate in its profits and its failures. A single stock can go to zero; that is why the unit of investing is rarely one stock.
Bond
A loan you make — to a government or a company — repaid with interest. Steadier than stocks, lower long-run returns. The stabilizer in a portfolio, not the engine.
Mutual fund
A pool that holds hundreds or thousands of stocks or bonds; you own a slice of the whole pool. Priced once a day after the market closes. The classic 403(b) building block.
ETF (exchange-traded fund)
The same pooling idea, but the fund itself trades on the exchange like a stock — intraday pricing, no minimums beyond one share, and a structure that tends to generate fewer taxable distributions in a taxable account.
Index fund
A mutual fund OR ETF that buys the entire market by rule (say, the S&P 500 or the total U.S. market) instead of paying managers to guess winners. Rock-bottom fees — often 0.03–0.05 percent — because there is nothing to pay a stock-picker for.
Expense ratio
The fund’s annual fee, quietly skimmed from your balance: 0.04 percent means $4 per $10,000 per year; 1 percent means $100. It is the single most reliable predictor of long-run fund performance — lower wins.
Evidence-based investing
Picking individual stocks on conviction is eminence-based medicine: confident, occasionally brilliant, unreproducible. An index fund is the guideline-driven protocol — it captures the outcome of the entire system and removes individual-judgment error. The data reads like a landmark trial: over 15-year periods, roughly nine in ten U.S. large-cap active funds trail the plain S&P 500 index after fees. When a cheap protocol beats the specialists nine times out of ten, you use the protocol.
You already know this framework — it is the one you practice medicine with.
~90% of U.S. large-cap active funds underperformed the S&P 500 over the trailing 15 years
This is the core empirical fact of retail investing, replicated year after year.
Source: S&P SPIVA scorecard
Mutual fund vs ETF
This step is a quick self-check. Open the full module to try it with your numbers →
What one percent actually costs
$100,000 invested for 30 years at a 7% gross return.
Bottom line: A fee that sounds like “one percent” consumes roughly a quarter of your ending wealth over a career. On physician-sized balances, fund selection inside the SAME account is a six-figure decision.
The 403(b) menu
This step is an interactive scenario. Open the full module to try it with your numbers →
Mutual fund vs ETF, side by side
Both can be excellent — the wrapper choice mostly follows the account type.
| Feature | Mutual fund | ETF | |
|---|---|---|---|
| Pricing | Pricing | Once daily at NAV | All day on exchange |
| Minimums | Minimums | Often $1,000–3,000 | One share |
| Auto-invest from payroll | Auto-invest from payroll | Automatic (403b/401k standard) | Clunkier |
| Tax efficiency (taxable acct) | Tax efficiency (taxable acct) | Good if index | Usually best |
| Index versions available | Index versions available | Yes | Yes |
What to do this week
- A fund is a basket; mutual fund vs ETF is packaging. Index vs active — and the expense ratio — is what matters.
- Index funds beat roughly nine of ten professionals over 15 years, after fees. That is the base rate you are betting against with active funds.
- Expense ratios compound: 1 percent vs 0.04 percent on $100,000 is about $178,000 over 30 years.
- Inside a 403(b)/401(k), mutual-fund index funds are the natural fit; in a taxable brokerage, ETFs usually win on taxes.
- Risk lives in what a fund holds, not in how it trades.
Do this next: Log into your 403(b) and write down the expense ratio of every fund you currently hold. Anything near 1 percent should have to justify itself against a 0.04 percent index fund — it almost never can.
Run this with your own numbers
The interactive version of this lesson works through your actual paycheck, loans, and benchmarks — and your AI advisor can take it from there. Free to start, no card required.
Keep reading
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The Backdoor Roth IRA
Congress closed the front door. Physicians use the back door. Completely legal. Worth $7,500 of tax-free growth per year — forever.
Compounding on a Physician Timeline
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