You've probably heard the golden rule of investing: diversify, diversify, diversify.

Rather than relying on a single company, sector or country, investors spread their money across different assets so that one poor-performing investment doesn't derail their entire portfolio.

Diversification can't eliminate risk, but it can reduce volatility and help smooth returns over the long run.

That's where portfolio allocation comes in. Portfolio allocation is the process of dividing your investments among different asset classes, typically stocks, bonds and cash, to balance growth potential with risk. Rather than trying to predict the next winning stock or perfectly time the market, it focuses on building a portfolio that reflects your financial goals, investment horizon and tolerance for risk.

Portfolio allocation also helps address one of the biggest threats to long-term investment success: investor behavior. During market downturns, investors with portfolios that match their risk tolerance are generally more likely to stay invested, while those who have taken on too much risk often sell at the worst possible time. Over decades, maintaining a disciplined investment plan has historically mattered far more than chasing last year's best-performing investment.

For investors in Spain, portfolio allocation also involves decisions beyond choosing an asset mix. Local tax rules, the choice between ETFs and Spanish mutual funds, and the tendency to overweight domestic investments can all influence how a portfolio should be constructed. We'll cover those considerations before exploring seven portfolio allocation strategies that can help investors build a diversified, long-term portfolio.

Portfolio allocation at a glance

Portfolio allocation for investors in Spain

Although the principles of diversification are universal, investors in Spain face a few considerations that make portfolio construction slightly different from investors elsewhere. First, the most significant is the tax treatment of Spanish investment funds known as the traspaso system.

Take advantage of Spain's tax rules

Eligible Spanish mutual funds generally allow investors to transfer money between funds through the traspaso system without immediately paying capital gains tax. Taxes are typically deferred until the investment is eventually sold. Exchange-traded funds (ETFs), by contrast, generally do not qualify for this tax deferral under current Spanish rules.

That doesn't necessarily make one investment vehicle better than the other. ETFs often offer lower costs, greater transparency and a wider range of investment strategies, while Spanish mutual funds can provide valuable tax flexibility for investors who expect to rebalance frequently. The right choice depends on your investing style rather than a single feature.

Avoid home bias

Another common challenge is home bias—the tendency to invest disproportionately in companies and assets from your own country. Many households in Spain already have significant exposure to the domestic economy through employment, real estate or business ownership. Concentrating financial investments in Spanish equities as well can increase exposure to the same economic risks.

Although the IBEX 35 includes many globally recognized companies, Spain represents only a small fraction of the global equity market. A diversified global equity fund provides exposure to thousands of businesses across North America, Europe, Asia and emerging markets, reducing dependence on the performance of any single economy.

Keep short-term cash separate

Cash management also deserves separate consideration. Money intended for an emergency fund or expenses over the next few years generally shouldn't be invested alongside long-term retirement savings. High-yield savings accounts and money market funds (could be eligible for tax deferral—read more) can provide liquidity while reducing the need to sell long-term investments during periods of market stress.

Diversification doesn't have to be exciting

Finally, remember that diversification extends beyond geography. A well-diversified portfolio spreads investments across countries, industries and company sizes rather than relying on a handful of familiar names or the latest market trend.

That approach may sound boring, but boring investing has historically been one of the most reliable ways to build long-term wealth. Investors who consistently own diversified portfolios often outperform those who spend years chasing the next hot stock, sector or IPO (why overhyped IPOs may not be the best investment).

Seven portfolio allocation strategies

There isn't a single "best" portfolio allocation, and anyone claiming otherwise is probably oversimplifying. The right mix of investments depends on your age, financial goals, investment horizon and ability to tolerate market volatility.

That said, not every strategy deserves equal consideration. Some have stood the test of time because they're simple, broadly diversified and easy to stick with through changing market conditions. Others are better suited to specific stages of life or require a more hands-on approach. The goal isn't to find the most sophisticated portfolio—it's to build one you can confidently maintain through bull markets and bear markets alike.

Below are seven of the most widely used portfolio allocation strategies, along with who they're best suited for and the trade-offs investors should understand.

1. Warren Buffett's 90/10 portfolio

One of the simplest portfolio allocation strategies comes from legendary investor Warren Buffett. In his 2013 letter to Berkshire Hathaway shareholders, Buffett revealed that he had instructed the trustee managing his wife's inheritance to invest 90% in a low-cost S&P 500 index fund and 10% in short-term U.S. Treasury securities.

The recommendation reflects Buffett's long-standing belief that most investors are better served by owning the market through inexpensive index funds than by trying to outperform it through stock picking.

A portfolio with 90% invested in equities is designed to maximize long-term growth, not minimize short-term volatility. Investors following this approach should expect significant market swings and be comfortable seeing their portfolio decline during bear markets without changing course. The small allocation to government bonds provides liquidity and a modest cushion against volatility, but it does little to reduce overall portfolio risk.

Buffett's recommendation is straightforward, but it's also more aggressive than many investors realize. For younger investors with decades before retirement, that level of equity exposure may be entirely appropriate. 

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For investors approaching retirement or anyone uncomfortable with large fluctuations in portfolio value, a more balanced allocation may prove easier to stick with over time.

Example allocation

• 90% global equity index fund

• 10% short-term government bond fund

2. The 80/20 growth portfolio

The 80/20 portfolio takes a similar approach but introduces a larger allocation to fixed income, creating a portfolio that remains growth-oriented while offering greater diversification.

With 80% invested in equities and 20% in bonds, investors retain most of the long-term return potential associated with the stock market while reducing some of the portfolio's overall volatility. Although bonds won't eliminate losses during market downturns, they have historically helped cushion declines and provide a source of stability when equity markets become turbulent.

For investors still decades from retirement, the 80/20 portfolio strikes a compelling balance between growth and risk management. It offers much of the upside of an all-equity portfolio without requiring investors to accept quite the same level of volatility.

If there were a default allocation for younger long-term investors, this would be one of the strongest candidates.

Example allocation

• 80% global equities

• 20% investment-grade government and corporate bonds

3. The traditional 60/40 portfolio

For decades, the 60/40 portfolio served as the standard recommendation for investors seeking a balance between long-term growth and capital preservation.

The logic is straightforward. Equities provide the portfolio's growth engine, while bonds help reduce volatility and can provide income during periods of market uncertainty. Historically, the two asset classes have often behaved differently enough that bonds softened the impact of equity market declines.

The strategy faced renewed criticism after both stocks and bonds declined sharply during 2022, leading some commentators to question whether the traditional 60/40 portfolio had become obsolete. Those predictions have largely proved premature.

Although no allocation performs well in every market environment, the 60/40 portfolio remains one of the simplest and most effective ways to build a diversified portfolio. It continues to form the foundation of many professionally managed retirement portfolios because it prioritizes consistency over chasing the highest possible returns.

For investors with moderate risk tolerance, or those approaching retirement, it remains a sensible starting point.

Example allocation

• 60% global equities

• 40% high-quality bonds

4. Age-based portfolio allocation

Some investors prefer a strategy that gradually becomes more conservative over time rather than maintaining the same allocation throughout their investing lives.

One of the most common rules of thumb is "110 minus your age." Under this approach, a 30-year-old would allocate roughly 80% of their portfolio to equities and 20% to bonds, while a 60-year-old would reduce equity exposure to around 50%.

More aggressive variations use 120 minus your age, reflecting longer life expectancies and the expectation that retirement portfolios may need to continue growing for several decades.

Age-based formulas are popular because they're easy to understand, but they shouldn't be followed mechanically. Two investors of the same age can have very different financial goals, income security and tolerance for risk. Someone with a generous pension, for example, may be comfortable maintaining a higher equity allocation than someone who expects to rely heavily on their investment portfolio for retirement income.

Think of these rules as useful guidelines rather than precise formulas.

5. The three-bucket strategy

Unlike the other approaches on this list, the three-bucket strategy organizes investments according to when the money will be needed rather than by asset class alone.

The first bucket typically holds cash or money market funds to cover near-term spending. The second contains bonds intended for medium-term expenses, while the third remains invested primarily in equities to support long-term growth.

The strategy has become particularly popular among retirees because it helps separate short-term spending needs from long-term investments. Instead of selling equities after a market decline to fund everyday expenses, retirees can draw from their cash bucket while giving the equity portion of the portfolio time to recover.

The three-bucket approach isn't necessarily designed to maximize returns. Its greatest strength is behavioral. By creating a clear plan for spending during market downturns, it can make it easier for investors to remain disciplined during periods of volatility.

A typical three-bucket portfolio might include:

• Bucket 1: Cash or money market funds for one to three years of spending

• Bucket 2: High-quality bonds for medium-term needs

• Bucket 3: Global equities for long-term growth

6. The core-satellite portfolio

Core-satellite investing combines passive investing with a limited amount of active management.

The majority of the portfolio, the “core,” is invested in broadly diversified, low-cost index funds that provide exposure to global markets. A smaller portion, the “satellite,” is allocated to investments where the investor has higher conviction, such as individual stocks, thematic ETFs or sector funds.

The appeal is easy to understand. Investors can pursue ideas they believe in without sacrificing the diversification that comes from broad market exposure.

The approach works best when the satellite remains genuinely small. It's surprisingly easy for a handful of successful individual investments to grow into an outsized share of a portfolio, increasing concentration risk over time. Periodic rebalancing helps ensure that the core continues to do most of the heavy lifting.

For experienced investors who enjoy researching individual companies or investment themes, the core-satellite approach can provide flexibility without fundamentally changing the portfolio's risk profile.

Example allocation

• 85% global index funds

• 10% individual stocks

• 5% thematic or sector ETFs

7. A customized portfolio based on your goals

Ultimately, no portfolio allocation strategy should take precedence over your own financial objectives. An investor saving for a home purchase in five years is likely to require a much more conservative allocation than someone investing exclusively for retirement 30 years from now. Likewise, investors with substantial emergency savings and stable incomes may be comfortable accepting greater market volatility than those who expect to draw on their investments in the near future.

This is why professional financial advisors rarely begin with a portfolio model. They begin by understanding a client's goals, time horizon and tolerance for risk before recommending an allocation. The same principle applies whether you're managing your own investments or working with an advisor.

A portfolio should fit your life, not the other way around.