Chapter 13: Diversification, fees, and rebalancing
Three quiet habits decide most of your investing results: spread your bets, keep costs low, and rebalance on a rule instead of a feeling. Together they take about an hour a year. Ignore just one of them, fees, and a 1% annual charge can eat about a quarter of your wealth over 30 years. This chapter shows you the math, then gives you the rules.
Diversify across the things that can fail together
Diversification means spreading your money so that no single failure can break your plan. Most people hear the word and think "own a lot of stocks." That's only the first item on the list. The real question is what could fail together?
- Companies. One company can go to zero. A fund holding thousands cannot, unless the whole economy does.
- Sectors. Tech, energy, banks: whole industries have bad decades. A fund that holds only one sector is not diversified, no matter how many stocks are inside it (Investor.gov makes this point directly).
- Countries. The US is one market. Most of the world's companies are elsewhere.
- Asset classes. Stocks and bonds usually fail at different times. That's the point of owning both (Chapter 12).
- Your employer. This is the one people miss. Your paycheck, your health insurance, and maybe a pile of company stock all depend on one employer. Maya holds $460,000 of her company's stock out of an $820,000 portfolio, so 56% of her investments ride on the company that also pays her salary. One bad year there hits everything at once. We untangle her situation fully in Chapter 18.
- Property. A house is a large bet on one building in one neighborhood.
- Tax treatment. Spreading money across traditional, Roth, and taxable accounts (Chapter 16) diversifies you against future tax rates.
A portfolio of five funds that all hold the same 500 US companies is one bet wearing five costumes. Look at what's inside the funds, not how many you own.
What the evidence says about picking stocks
An index fund is a fund that simply buys every company in a market list (the whole haystack instead of hunting the needle) for a very low fee. The alternative is picking stocks yourself or paying a manager to pick them.
The best-known study here is Barber and Odean's "Trading Is Hazardous to Your Wealth" (2000). They examined tens of thousands of households at a brokerage and found the most frequent traders underperformed the market by about 6.5 percentage points a year over the period studied. The lesson is not that no one can ever pick a winner. The lesson is that trading costs, taxes, and overconfidence stack the deck: the more you trade, the more those costs compound against you.
If you enjoy picking, there's a sane way to do it: core-and-explore. Your core, the large majority of your portfolio, sits in broad, cheap index funds. Your explore money is capped at an amount whose total loss would change nothing about your life. For most people that's 5% or less of the portfolio.
Diversify across everything that can fail together: companies, sectors, countries, asset classes, your employer, and tax treatment. Cap speculative picks at an amount whose total loss would not change a single goal or date in your plan.
Fees compound in reverse
Compounding (Chapter 11) is the engine of investing. A fee is the same engine running against you: it takes a slice every single year, and every slice it takes stops growing for you forever.
The expense ratio is the annual fee a fund charges, taken silently out of your returns; you never see a bill. A broad index fund can cost 0.05% a year or less. Some funds charge 1% or more for the same job.
The standard illustration from Investor.gov: $100,000 invested for 20 years, growing 4% a year.
$100,000 growing 4% a year for 20 years, with a low-cost fund.
Same money, same market, same 20 years. The fee quietly ate about $29,000.
At 0.50%, you'd end near $198,000; every quarter-point matters. And the bite grows with time: over 30 years, the gap between earning 7% and earning 7% minus a 1% fee is about 25% of your final wealth. A 1% fee doesn't sound like much because it's quoted against your whole balance, not against your returns. If your portfolio earns 6% and the fee is 1%, the fee is taking one-sixth of everything you make that year.
Watch for fees stacking: an advisor charging 1% of assets who puts you in funds charging 0.8% has you paying 1.8% a year. Always ask for the all-in cost: every layer added together, in dollars.
Try the calculator above with your own balance, timeline, and fee. The gap is usually bigger than people guess.
Rebalancing: sell high, buy low, on a schedule
Say your plan calls for 70% stocks and 30% bonds, and you hold $100,000. Then stocks have a great year and rise 30% while bonds stay flat: you now have $91,000 in stocks and $30,000 in bonds, a 75/25 portfolio. You didn't decide anything, but you now hold more risk than you chose, right after prices got more expensive. Rebalancing means trading back to your target mix. It forces you to trim what just grew and add to what just lagged: selling high and buying low, by rule rather than by nerve. It will almost always feel wrong in the moment; that's how you know it's working.
Pick one of three rules and write it down:
- Calendar. Rebalance once a year, on a date you'll remember. Simple, good enough for almost everyone.
- Threshold bands. Rebalance only when an asset drifts more than a set amount (say 5 percentage points) from target. Fewer trades, slightly more attention.
- Cash-flow steering. Direct every new contribution to whatever is below target. In a taxable account this is the best trick of all, because you fix your mix without selling anything, and selling is what creates capital gains taxes (Chapter 15).
What you must not do is rebalance by feel. "I'll trim stocks when it seems toppy" is market timing with a calmer name, not rebalancing. And don't over-rebalance, either: checking weekly and trading monthly adds taxes and trading costs for almost no risk benefit. Once a year, or at a 5-point drift, is plenty.
Rebalance on a written rule (once a year, at a 5-point drift, or with new contributions), never on a mood. In taxable accounts, steer new money first so you don't trigger gains.
Maya thought she was diversified: she owns a $300,000 broad US stock fund and $60,000 in bonds. Then she added up the $460,000 of employer stock: 56% of her $820,000 portfolio in one company, the same company that pays her $220,000 salary and grants her RSUs. Her stocks-versus-bonds mix was fine; her real risk was concentration. So her first rebalancing rule has nothing to do with bonds. It's a written cap on employer stock, which she'll build in Chapter 18.
Where people go wrong
- Collecting funds instead of diversifying. Five funds holding the same big US companies is one bet, counted five times.
- Judging funds by last year's return. Past performance shifts constantly; fees are reliable. Cost is the strongest single predictor you control.
- Ignoring "small" fees. 1% sounds tiny. Over 30 years it's roughly a quarter of your ending wealth.
- Treating employer stock as loyalty. The company already controls your paycheck. It doesn't need your portfolio too.
Key takeaways
- Diversify across everything that can fail together: companies, sectors, countries, asset classes, and especially your employer.
- The evidence is blunt: frequent traders in the classic Barber-Odean study trailed the market by about 6.5 points a year. The cause was costs and overconfidence, not bad luck.
- Fees compound in reverse: on $100,000 over 20 years, a 1.00% fee instead of 0.25% costs about $29,000 (Investor.gov). Always ask for the all-in cost in dollars.
- Cap speculative picks at an amount whose total loss changes nothing.
- Rebalance by written rule (calendar, threshold, or new contributions), never by feel.
Sources: Investor.gov: Understanding Fees · Investor.gov: Asset Allocation · Barber & Odean (2000), "Trading Is Hazardous to Your Wealth"