How Should a Physical Therapist, OT, or SLP Invest?

How should a physical therapist, OT, or SLP invest? It's really quite simple. Buy a few low-cost index funds that own the whole market, hold them in the right accounts, and add to them every month for years. You don't pick individual stocks or try to time the market. You choose the approach once, set it, and forget it.

Key takeaways

• Index funds outperform stock picking. Over 10 to 15 years most professional managers lose to a plain index, so owning the whole market is the higher-odds bet.
• Keep fees near zero. A 1% annual fee can cost six figures over a career; a broad index fund charges almost nothing.
• Savings rate is the most important number. At a 7% return after inflation, $500 a month becomes about $610,000 in 30 years, and $1,000 a month about $1.22 million.
• Automate it, and don't sell in a downturn. A market drop just buys you more shares on sale; selling at the bottom turns a dip into a permanent loss.
• Target-date funds are a fine default, but not for early retirement. One fund that auto-diversifies and rebalances is great while you're working, but it transitions to conservative around age 65; if you're retiring early and drawing down, set your allocation by hand.
• Stay heavy in stocks while you're working. Bonds earn their place only as you approach living off the portfolio.
• The accounts matter as much as the funds. Capture the employer match, max out your tax-advantaged accounts, then invest the rest in a taxable account.

What's in this guide

• Why invest at all
• Why index funds beat picking stocks
• Expense ratios: the fee that compounds against you
• Dollar-cost averaging: just keep buying
• Diversification: own everything
• Target-date funds: the one-fund option
• How to pick funds inside your 401(k) or 403(b)
• Growth vs. preservation: how your mix changes over time
• Where this money lives: accounts in brief
• Next steps

Why invest at all

You already did the hard part. Phase 1 was about widening the gap between what you earn and what you spend: paying down loans, cutting the big expenses, getting an emergency buffer in place. That gap is your savings rate, and it has to go somewhere. If you leave it in a checking account it loses ground to inflation every year. Invested money compounds.

Here is what compounding looks like on a therapist salary. Put $500 a month into a broad stock index fund and leave it alone for 30 years. At a 7% return after inflation, you end up with about $610,000. You contributed $180,000 of that; the other $430,000 is growth. Double the contribution to $1,000 a month and you land near $1.22 million.

30 years at a 7% return after inflation. Growth is the portion you didn't contribute.

The balance buys options. As that portfolio grows, it starts buying you power: to drop to PRN, take a sabbatical, walk away from a clinic that's grinding you down, or stop working entirely and retire. The portfolio is the engine that makes the options possible.

Why index funds beat picking stocks

A market index, like the S&P 500, is a list of companies. An index fund buys stock in all of those companies in the same proportions the index uses. If you buy a share of the S&P 500 for instance, you are essentially buying small fractions of the top 500 companies in the US. No one picks which stocks will win; the fund simply holds the entire list. Index funds are therefore cheap to manage and typically have very affordable fees. Alternatively, an actively managed fund takes the opposite approach: a manager and a research team pick stocks and trade them in an attempt to beat the market, charging higher fees for that effort.

For the average investor (such as rehab clinicians), there is a strong case to be made for investing in index funds over managed funds. S&P's SPIVA scorecard tracks how active funds perform against a plain index. Through year-end 2024, about 83% of actively managed U.S. large-cap funds underperformed the S&P 500 over the prior 10 years, and over 15 years not a single category had a majority of active managers beating their benchmark (SPIVA U.S. Year-End 2024, S&P Dow Jones Indices). These are full-time professionals with research teams, and most of them lose to simple index funds that charge almost nothing. So you don't try to beat the market. Instead, buy the entire market with index funds.

The funds are the easy part. The hard part is being consistent and reducing the urge to actively buy/sell when things go sideways. The biggest threat to your returns is the urge to act, and it gets loudest exactly when you should do nothing. When the market is climbing, fear of missing out tells your brain to buy more. When it drops, fear of losing more pushes you to sell near the bottom. Buy high, sell low, the fastest way to lose money. Studies of how people actually behave consistently find that the returns investors earn trail the returns of the funds they hold. Over the decade ending in 2023, the average fund investor earned about 1.1 percentage points a year less than the funds they owned, roughly 15% of the return, lost to badly timed buying and selling (Morningstar, Mind the Gap 2024).

The discipline that makes index investing work is doing nothing during a downturn. A 30% drop only becomes a loss if you sell into it. Keep your money in, keep buying. A 30% drop means you're getting a 30% discount on your new contributions. Who doesn't love a good sale?

Expense ratios: the fee that compounds against you

Every fund charges an expense ratio, an annual cut of your money. A broad index fund might charge 0.04%. An actively managed fund often charges 0.75% to 1.0% or more. The percentages look trivial, but once you calculate them out over the long-term, they can seriously impact your portfolio.

Take $250,000 invested for 30 years at a 7% return before fees, and watch what the fee alone does.

Single $250,000 balance growing at 7% before fees for 30 years, fees deducted annually. Lost to fees is measured against a hypothetical zero-fee fund (~$1.90M).

That simple decision to choose an index fund instead of an actively managed fund just earned you the price of a house. All while outperforming most actively managed funds. Seems like a no-brainer to me.

Dollar-cost averaging: just keep buying

If you invest a fixed amount on a fixed schedule, automatically, you are "dollar-cost averaging." You buy more shares when prices are low and fewer when prices are high, without thinking about it. For someone investing out of a paycheck, it is simply how the money goes in when you allot a certain dollar amount to investing every month.

The advantage shows up in a downturn. When the market drops, your fixed monthly buy picks up more shares at the lower price. You are buying on sale. The headline that scares everyone ("market falls X%") is, for someone still adding money, the best buying window you get. I personally get excited when I hear the news of a downturn now. When others are panic-selling, I'm excited to have the opportunity to buy discounted shares for a while.

One honest caveat. If a lump sum lands in your lap (an inheritance, a bonus, a 401(k) rollover), the data says investing it all at once usually beats spreading it out. This is contrary to a lot of internet advice out there. Vanguard found lump-sum investing beat dollar-cost averaging about two-thirds of the time, because markets rise more often than they fall (Vanguard, Cost averaging: Invest now or temporarily hold your cash?, 2023). But for the therapist contributing month-to-month from their paycheck, dollar-cost averaging is the best method.

Diversification: own everything

Diversification means not putting your future in the hands of one company or one sector. Own a single stock and that company's bad year can tank your portfolio. Own the whole market and any one company barely registers. There are three building blocks to a well-diversified portfolio:

• U.S. stocks are ownership stakes in American companies. This is your growth engine: highest expected return over time, but with significant volatility in the short-term. A bumpy but fast ride to growth.
• International stocks are the same idea for companies outside the U.S. They sit in the portfolio because the U.S. will not lead forever, and when it lags it can lag for years. International stocks mitigate this risk.
• Bonds are loans to governments or corporations that pay interest. Lower return, lower volatility. Their job is to preserve wealth. (Bonds have their own section below).

The default most index investors land on is the three-fund portfolio: a total U.S. market fund, an international fund, and a bond fund, in some ratio. It is cheap, it owns nearly every public company on earth, and over multi-decade periods it has out performed the large majority of stock-picking and actively managed strategies, for the same reason laid out in the evidence section.

One live debate is worth knowing before you copy anyone's allocation: how much international to hold, if any. A large camp argues for 100% U.S. stock allocation. Since, big American companies already earn much of their revenue overseas, you get global exposure without a separate fund; costs are rock-bottom; and U.S. stocks have outrun international for most of the past 15 years. Vanguard founder John Bogle was comfortable with a U.S.-only stock portfolio. The other camp keeps 15% to 40% of stocks international, on the logic that U.S. dominance isn't permanent and reversals run long. Both are defensible, and a U.S.-only version (U.S. stocks plus bonds) still follows the same three-fund logic.

How to pick funds inside your 401(k) or 403(b)

For therapists, we typically start investing by funding our employer-sponsored 401(k) or 403(b) plans. Inside an employer plan, you only get the menu your employer chose, and therapy-employer menus are often mediocre: a short list, high fees, few good index options.

When looking through the fund options, here are a couple of tips:

1. Look at the expense ratio first and what companies the fund actually holds.
2. Find the cheapest broad index option on the list, usually something with "total market," "S&P 500," or "index" in the name and an expense ratio under about 0.20%. Most employer plans have some variation of a US-based index fund with low expense ratios.

If the whole list of funds is genuinely bad, contribute just enough to capture the full employer match (free money), then do the rest of your investing in an account you control, like a Roth Individual Retirement Account (IRA). Learn which accounts to start with in the separate guide.

Picking your own funds comes with one job: rebalancing. If you build your own mix (say 60% U.S., 30% international, 10% bonds), markets will pull those percentages out of line as one piece grows faster than another. Rebalancing is just resetting them back to the target ratio. Most investors do this about once a year and automate it to avoid the "tinkering effect" as described above. If that sounds like a chore, you may prefer a target-date fund, which rebalances itself.

Target-date funds: the one-fund option

If picking and maintaining a mix sounds like more than you want to deal with, there is a set-and-forget version: a target-date fund. You pick the fund with the year closest to when you'll want the money ("Target 2050"), and it holds a diversified mix for you, slowly shifting toward bonds as that year approaches. One fund, fully diversified, and self-adjusting. It's the easiest way to ensure you are not tinkering and allowing the market to compound without you ever thinking about it.

Before you commit to a target date fund, two things to check:

First, the expense ratio. Some target-date funds are very cheap, others bundle in high fees, which can eat a huge chunk out of your portfolio as demonstrated above.

Second, the target year. These funds glide toward a traditional retirement age, so an early timeline complicates the decision, and the right move depends on whether you'll be drawing from the portfolio earlier than typical retirement age. If you're coasting or part-time and not yet living off it, you want to stay aggressive, so a later target year fits. If you're going to fully retire early and live off the portfolio, a single target-date fund is a bit awkward: an earlier target year puts bonds in place for sequence risk, but can leave you too conservative for a retirement that may run 40 years or more. At that point the allocation is better set by hand rather than with a target-date fund (see growth vs. preservation below).

Growth vs. preservation: how your mix changes over time

The mix depends on one question: are you adding to the portfolio, or living off it?

While you're working, investing, or coasting on part-time or PRN income, stay heavy in stocks, up to 100%. You have years before you touch the money, so you can ride out market corrections and treat them as buying opportunities. A bad year on paper does no lasting damage when you aren't selling.

The mix only changes once you are living off the portfolio. The danger then is sequence risk: a large drop in the market in your first few withdrawal years, while you're selling shares to cover your life, can do damage you never recover from. To prevent this, you hold a buffer of a few years' expenses in bonds or cash that you spend from instead of selling stocks at the bottom. That buffer is the main reason to hold bonds.

Retiring early doesn't flip you to a conservative portfolio, contrary to some of the advice out there. An early retirement that may require 40 years or more of withdrawals still needs the growth only stocks provide, so early retirees stay stock-heavy, holding bonds as a small early-years buffer while the rest stays in stocks. The longer your horizon, the more you keep in stocks.

Where this money lives: accounts in brief

Tax optimization is equivalent to putting a turbocharger on your investing engine. Knowing where to put these funds can result in hundreds of thousands of dollars in your portfolio, instead of in the hands of the government. Each account has its own tax rules:

Roth example assumes monthly contributions at a 7% after-inflation return.

For almost everyone, the order to fill these is the same:

1. Capture the full employer match. Put enough into your 401(k) or 403(b) to get every dollar your employer matches. It's an instant return nothing else comes close to.
2. Max your tax-advantaged accounts. An IRA (Roth or traditional), your 401(k) or 403(b) beyond the match, and a Health Savings Account (HSA) if you have a high-deductible health plan. These shelter you from taxes in different ways.
3. Then a taxable brokerage account. Once the tax-advantaged accounts are full, the rest goes here. It has no contribution limit and no early-withdrawal penalty, which makes it the bridge that funds an early retirement before age 59½.

Why this order, how much it saves in taxes, and the edge cases (Roth vs. traditional, the 457(b) some hospital employees can tap before 59½, the backdoor Roth) are in the where to invest guide. If you're on an income-driven student loan plan, traditional contributions also lower your AGI, which has its own use case.

Next steps

The big picture: buy low-cost index funds, keep your fees near zero, add money every month and especially when the market drops, diversify across the market, and hold the right accounts in the right order. The rest is being consistent and leaving the funds alone.

From here, run your own numbers in the Investment Calculator to see what a monthly contribution becomes over time. Then pick the accounts to hold it in with the companion guide on where to invest. And when you want to see what options your portfolio can buy, measured in years rather than dollars, read the financial autonomy guide.

Common questions

How should a physical therapist, OT, or SLP invest?

Buy low-cost index funds that own the whole market, hold them in tax-advantaged accounts, and add to them every month. You don't need to pick individual stocks or time the market. Over long periods a plain index beats most professional fund managers, and keeping fees near zero leaves far more in your account. Choose the approach once and stay consistent.

Are index funds better than actively managed funds?

For most investors, yes. Through year-end 2024, about 83% of active U.S. large-cap funds underperformed the S&P 500 over the prior 10 years, and over 15 years no category had a majority of active managers beat their benchmark (S&P SPIVA). Active funds also charge much higher fees, which compound against you for decades. A broad index fund captures the market's return at almost no cost.

How much should I invest each month?

As much of the gap between what you earn and what you spend as you can sustain. The amount you contribute matters more than any other lever. At a 7% return after inflation, $500 a month for 30 years grows to about $610,000, and $1,000 a month grows to about $1.22 million. Start with what you can automate now and raise it as your income grows.

What index fund should I start with?

A broad, low-cost one. Look for a total U.S. market fund or an S&P 500 fund with an expense ratio under about 0.20%. If you would rather make one decision and never rebalance, a target-date fund holds a diversified mix and adjusts it for you over time. Check its expense ratio first, since some are cheap and some are not.

Should I hold bonds or invest 100% in stocks?

While you are still working and adding money, a heavy stock allocation, up to 100%, is defensible, because you have years to ride out drops and you are not selling. Bonds earn their place as you approach living off the portfolio, where a bad early year can do lasting damage. The "bonds are dead" talk traces to 2022, when stocks and bonds fell together, but that relationship normalized through 2025.

Is now a good time to start investing?

The best time is when you have money to invest, not when the market looks calm. Trying to time your entry usually costs more than it saves, because markets rise more often than they fall. If you invest a fixed amount every month, a market drop simply buys you more shares at lower prices. Time in the market matters more than timing it.

This is Phase 2, Step 2 of Build the Runway: invest in low-cost index funds.
Next → Where to invest: the right accounts.

Disclaimer

I'm a physical therapist, not a financial advisor, and this is not financial advice. It's what I learned building my own plan, shared so you can think through yours. For decisions specific to your situation, talk to a fee-only fiduciary advisor or a tax professional.