Bond ETFs: what they do in a portfolio

When people start investing, they almost always think about stocks: Apple, Mercado Libre, an S&P 500 ETF. Bonds sound boring. But in a portfolio they play a role stocks can't: cushioning the falls. Understanding how they work is one of the simplest ways to build a portfolio you can stick with through the bad years.

What a bond is

A bond is a loan. When you buy a bond, you lend money to a government or a company. In return, it pays you interest (the coupon) and gives your capital back on a fixed date (maturity).

Buying bonds one by one is complicated: minimum amounts are high and every country has its own rules. That's why most investors use bond ETFs, funds that trade on an exchange like a stock and hold hundreds or thousands of bonds.

Why bonds lower risk

There are two main reasons:

1. They move less. An intermediate-term government bond ETF usually has annual volatility of 4% to 7%. A stock ETF, 15% to 20%. Even a small slice of bonds lowers total volatility noticeably.
2. They often move differently. In several crises, when stocks fell, government bonds rose as investors looked for safety. That low or negative correlation is what helps diversification the most. We explain it in detail in correlation and diversification.

Careful: the relationship isn't fixed. In 2022, for example, inflation pushed interest rates up and stocks and bonds fell together. Bonds reduce risk, but they don't eliminate it.

Types of bond ETFs

Not all bonds are alike. These are the differences that matter most:

Type	Examples	Risk	What to expect
Government, short term	SHY	Very low	Little return, almost no bumps
Government, intermediate term	IEF, GOVT	Low	The classic "safe haven"
Government, long term	TLT	Medium-high	Very sensitive to interest rates
Aggregate (whole market)	BND, AGG	Low	Mix of government and corporate
Investment-grade corporate	LQD	Low-medium	A bit more return than government
High yield	HYG	Medium	Behaves a lot like stocks
Inflation-protected	TIP	Low-medium	Principal adjusts with US inflation
Emerging markets in dollars	EMB, VWOB	Medium	Emerging-country debt, no direct currency risk
Emerging markets in local currency	EMLC, LEMB	Medium-high	Adds emerging-currency risk

Two ideas to keep in mind:

• Term: the longer the maturity, the more a bond moves when rates change. This is called duration.
• Quality: bonds from companies or countries more likely to default pay more interest, but in crises they fall along with stocks. Don't expect a high-yield ETF to protect you in a bad year.

Bonds outside the United States

QuantMundi has 34 bond ETFs from several regions: the United States, Europe (for example euro-area and UK bonds), Japan, Canada, Australia, China, Chile and emerging-market debt funds.

If you invest from Latin America or anywhere outside the bond's currency, there's an important point: bonds in another currency carry currency risk. A euro bond can be very stable in euros, but measured in Colombian pesos or Brazilian reais, the exchange rate can move it far more than the bond itself. The optimizer does this math for you: it converts everything to your currency using each day's exchange rate. We explain it in currency risk.

Some international ETFs, like BNDX, are hedged: they neutralize the currency effect against the dollar. That's why they move much less than unhedged ones like BWX.

How much in bonds

There's no single right answer. Some rules used as a starting point:

• 60/40: 60% stocks and 40% bonds. The "classic" portfolio of many funds.
• By time horizon: if you'll need the money in a few years, more bonds; if decades away, you can tolerate more stocks.
• By how much you can stomach: if a 30% drop would make you sell everything, you need more bonds than you think.

The best mix is the one that lets you avoid panic selling when the market falls.