Free course · Investing · Beginner
Diversification: Building a Portfolio That Holds Up
A pile of stocks bought one at a time is a collection. Diversification turns it into a portfolio, by deciding how the pieces fit together and how much any one of them is allowed to hurt you.
- Lessons
- 4
- Time
- About 57 minutes
- Level
- Beginner
- Cost
- Free, no sign-up
Who it is for
Investors with a handful of holdings who want a plan for the portfolio as a whole, and a way to tell whether it is really spread out.
By the end you can
- Explain how one company's bad news can sink a concentrated portfolio, and do the loss-recovery sums
- Check how a set of holdings is spread across sectors, company sizes and countries
- Compare fund costs and overlap before building a core around them
- Set a target mix and bring a portfolio back to it when it drifts
Lessons
- 1 Concentration Risk: Why a Single Stock Is a Risky Portfolio
How concentration risk in one stock exposes you to lawsuits, failed products and fraud, why deep losses are hard to recover, and what spreading out can fix.
- 2 Sector Diversification: Spreading Across Sizes and Countries Too
How to check sector diversification with the 11 GICS sectors, then by company size and country, and why many stocks in one sector are really one bet.
- 3 Index Funds vs Individual Stocks: Building the Core
Index funds vs individual stocks: how funds spread money across many companies, what expense ratios cost in dollars, and how a core-and-satellite mix uses both.
- 4 Portfolio Rebalancing: Bringing the Mix Back in Line
Portfolio rebalancing explained: why a mix drifts from its target, how to calculate the trades that bring it back, and calendar versus threshold timing.
Maybe you own five stocks. You bought each one for a good reason, at a different time, and you have never looked at them side by side. That’s the situation the course starts from, and plenty of investors are in it. It also leaves questions nobody answered when the orders went in: how much of your money rides on a single company, whether the five really behave like five separate bets, and what you’d do if one of them doubled or halved.
Who it suits
It’s written for beginners who already own something, whether that’s a few individual stocks, a fund or two in a retirement plan, or a mix of both, and who want a plan for the whole portfolio. No finance background is assumed. You should know what a share is and how to place a buy order. That’s about it.
What to have ready
A list of what you own. For each holding, write down its current market value and the account it sits in, since a taxable brokerage account and a retirement account get treated differently when you sell. If you have a workplace retirement plan, pull its latest statement too. Holdings there count toward the total, and they are easy to leave off.
A spreadsheet helps. A sheet of paper works.
How to work through it
Take the lessons in order, one sitting each if you like. The whole set runs just under an hour. Each lesson asks you to do something to your own list, such as labeling each holding by sector or adding up what you pay in fund fees, and the course works far better if you actually do it, because a principle you’ve applied to your own account is much harder to forget than one you only read about, and by the end you’ll have a working plan.
Every allocation you’ll see, whether it’s a 60/40 split or a core of funds with a few stocks around it, is an example of how the arithmetic works. None of it is a recommendation. The right mix for you depends on how long you can leave the money invested and how large a loss you could sit through without selling at the bottom.
What it leaves out
The course doesn’t pick funds or stocks. It doesn’t cover bonds in depth, options hedges, or strategies for harvesting tax losses. It also stays general on tax; rules depend on the account and your situation, so check with a tax professional before selling anything large.
Where to go after it
To judge any single company you add, work through How to Evaluate a Stock. If the goal of the portfolio is income, the Dividend Income Portfolio course builds on the same ideas, and the explainer on how rising interest rates affect dividend stocks shows why income holdings can move together even across sectors. The dividend reinvestment calculator lets you test how reinvested payouts shift the mix over time. For everything else on long-term investing, start at the investing hub.
Readers also ask
How many stocks do you need to be diversified?
No official number exists. What counts is how different the holdings are and how much money sits in each, since many stocks from one sector, or one position that makes up most of the account, still leaves you concentrated. A broad index fund spreads money across many companies in a single purchase.
Is an index fund enough diversification?
A broad index fund covers many companies and every sector in its index, which deals well with company-specific risk. It holds only what the index holds, often a single country's stocks, and it stays fully exposed to a market-wide fall. Whether that is enough depends on your time horizon and how deep a drop you could hold through without selling.
Can you be too diversified?
In a practical sense, yes. Owning many overlapping funds, or dozens of stocks you cannot keep up with, adds cost and paperwork while spreading risk very little further, and it blurs what you actually own. Checking funds for overlap and keeping a list of each holding and its weight keeps a portfolio manageable.