How to decide the right mix of stocks and bonds for where you are in life — and exactly what to do once all the pieces are in place.
Parts 1 and 2 handled the setup.
Part 1 covered the employer match — the highest-probability, highest-return financial move most people never fully capture. Part 2 walked through opening a brokerage account: IRA types, brokerage selection, and the three-fund portfolio concept that forms the backbone of this whole approach.
Now comes the question we’ve been building toward.
You’ve opened an account. You’ve got money ready to invest. The brokerage is showing you a list of funds. How do you decide how much goes in each one?
That is what this post answers. By the end, you will know how to set your allocation, how to automate it, and — just as importantly — what you do not do once the plan is running.
The Most Important Decision Isn’t Which Funds
Most new investors spend a lot of energy on fund selection — which specific ticker, which brokerage, which fund family. That energy is mostly wasted. The three brokerages we covered in Part 2 (Fidelity, Schwab, Vanguard) all offer excellent index funds at nearly identical low costs. The specific fund matters far less than the category.
The decision that actually determines how your portfolio behaves is the one most people spend the least time on: how much goes in stocks, and how much goes in bonds.
This split is called your asset allocation — the proportion of your portfolio divided between higher-risk, higher-return investments (stocks) and lower-risk, lower-return investments (bonds). Here’s why it matters so much.
Stocks have produced dramatically better long-run returns than bonds — but they fall sharply during market downturns. The S&P 500 dropped about 50% during the 2008–2009 financial crisis. It dropped 34% in the first months of the COVID pandemic in 2020. It has experienced a decline of 10% or more in roughly two out of every five calendar years since 1928.
Every one of those declines eventually reversed. The investors who held through them — and kept contributing — captured the recovery. The investors who sold during the panic did not.
Bonds provide stability. They don’t grow as fast. But they don’t fall as sharply, either. During many stock market crashes, bonds hold their value or even rise. A portfolio with meaningful bonds gives you a smoother ride — at the cost of some long-term growth.
The right stock-to-bond split depends on two things: how long before you’ll need the money and how you’ll actually behave when your portfolio drops 30%. Both matter equally. An allocation that’s theoretically optimal but causes you to sell in a panic is worse than a more conservative allocation you can actually hold.
The Classic Rules of Thumb — and What They Really Mean
Jack Bogle himself suggested a useful starting rule: hold roughly your age in bonds.
If you’re 25, put 25% in bonds and 75% in stocks. If you’re 50, put 50% in bonds and 50% in stocks. If you’re 65, put 65% in bonds and 35% in stocks.
An older version of the same idea says to put 100 minus your age in stocks — which gets you to the same numbers from the other direction.
These rules are starting points, not laws. They do three things well: they increase your bond allocation automatically as you age, they reduce your exposure to market swings as retirement approaches, and they’re simple enough to actually follow.
What they don’t account for:
- Income stability. A government employee with a guaranteed pension can afford to take more stock risk than a freelancer with irregular income. The pension provides its own kind of bond-like stability.
- Risk tolerance. How do you actually respond to a market drop? If you sold anything during the 2020 crash or the 2022 decline, you need more bonds than a rule of thumb suggests.
- Other sources of income. A part-time business, rental income, or significant Social Security benefits reduce the amount of work your portfolio needs to do — which can justify holding more bonds as a buffer.
Use the age-based rules as a starting point. Adjust them based on what you actually know about yourself.
Three Life Stages, Three Starting Points
The following allocations are reference points — not prescriptions. Use them to orient yourself, then adjust based on the factors above. All are expressed in terms of the three Vanguard funds we’ve used throughout this series: VTSAX (total US stock market), VTIAX (total international stock market), and VBTLX (total bond market).
Early career — early to mid-20s, 35+ years to retirement
| Fund | Allocation | What It Represents |
|---|---|---|
| VTSAX (US stocks) | 70% | Strong long-term growth engine |
| VTIAX (International) | 20% | Global diversification |
| VBTLX (Bonds) | 10% | Light ballast; recovery time is long |
Total stocks: 90%. Total bonds: 10%.
At this stage, time is your primary asset. Even a sharp market drop — 40%, 50% — will almost certainly recover before you need the money. You can afford to own mostly stocks. The modest bond allocation (10%) provides just enough ballast to keep you from panic-selling during a brutal downturn. Even small exposure to bonds tends to make portfolios easier to hold psychologically during crashes.
Mid-career — late 40s, roughly 15–20 years to retirement
| Fund | Allocation | What It Represents |
|---|---|---|
| VTSAX (US stocks) | 55% | Still the primary growth driver |
| VTIAX (International) | 15% | Maintained global exposure |
| VBTLX (Bonds) | 30% | Real ballast — meaningful protection |
Total stocks: 70%. Total bonds: 30%.
You have less time to recover from a major market decline. A drop that would have fully recovered in six years might not recover before your first retirement withdrawal. The bond allocation is now doing real work — it reduces the severity of the worst years, which matters more as the runway shortens.
Near retirement — within 5–10 years
| Fund | Allocation | What It Represents |
|---|---|---|
| VTSAX (US stocks) | 35% | Still some growth potential |
| VTIAX (International) | 15% | Maintains diversification |
| VBTLX (Bonds) | 50% | Capital preservation takes priority |
Total stocks: 50%. Total bonds: 50%.
At this stage, the portfolio’s job is shifting. It still needs to grow — because you may live 30 years in retirement — but it needs to protect against the specific risk of a market crash right before or right after you stop working. Selling stocks at depressed prices in your first years of retirement is one of the most damaging things that can happen to a long-term plan. Higher bond exposure reduces that vulnerability.
One note on the US/international split: These allocations keep international at 15–20% of the total. The US stock market represents roughly 60% of global equity by size, so a heavier US weighting is a common and defensible choice. If you prefer to mirror the actual global market more precisely, increase the VTIAX allocation and reduce VTSAX proportionally. The Bogle Method series explains the full reasoning behind the US/international decision in Part 2: The Three-Fund Portfolio.
What to Do Once the Pieces Are in Place
Once you’ve set your allocation and made your initial purchases, there are four things to do. And they’re all simple.
1. Automate Your Contributions
Every major brokerage lets you schedule a recurring automatic investment — a fixed dollar amount transferred from your bank account each month and automatically invested in your chosen funds in your target proportions. At Vanguard it’s called an automatic investment plan. Fidelity and Schwab have identical setups.
Pick the amount you can commit to each month. Pick the date — typically right after your paycheck deposits. Set the fund allocations to match your target percentages. Then leave it alone.
This is how the strategy actually works in practice. The automatic contribution buys shares every month, regardless of what the market is doing. When prices are low, you buy more shares. When prices are high, you buy fewer. Averaged over time, your cost per share ends up somewhere in the middle — a result that is almost always better than waiting for a “good time” to buy.
More importantly: removing the monthly decision means you never have to ask whether to invest this month. The answer is always yes. It’s automatic.
2. Set a Rebalancing Trigger
Over time, the funds in your portfolio grow at different rates. After a strong year for US stocks, your 70% VTSAX target might be sitting at 76%. Your portfolio no longer matches what you decided it should be.
Rebalancing is the process of bringing it back. You sell a small amount of whatever has grown past its target and buy a small amount of whatever has fallen behind. The math is straightforward:
If your target is 70% VTSAX and you now hold 76%, you sell enough VTSAX to bring it back to 70% and use those funds to top up the others.
A simple rebalancing rule that works: check once a year and rebalance if any fund has drifted more than five percentage points from its target. If nothing has drifted more than five points, leave it alone.
The Bogle Method series shows exactly how to do this with real numbers — full worked example, including the tax considerations for taxable accounts:
The Bogle Method, Part 3: Putting It Together
3. Know Where Each Fund Lives — Tax Location
Once you have more than one type of account (say, an IRA plus a taxable brokerage), the location of each fund matters.
The principle is straightforward: put your most tax-inefficient investments in accounts where taxes are deferred or eliminated.
- VBTLX (bonds) generates regular interest income, which is taxed as ordinary income — the highest rate. It belongs in a tax-advantaged account (IRA, 401(k)) where that income isn’t taxed each year.
- VTSAX (US stocks) is tax-efficient. Index funds rarely sell holdings, so taxable gains are rare. It can live in either type of account comfortably.
- VTIAX (international stocks) generates something useful: a foreign tax credit — a credit for taxes the fund pays to foreign governments that you can apply against your US tax bill. This credit is only available if the fund sits in a taxable account. In an IRA, the credit is lost.
In practice:
| Account Type | What Goes There |
|---|---|
| 401(k) / IRA | VBTLX (bonds) |
| Taxable account | VTIAX (international stocks) |
| Either | VTSAX (US stocks) |
If you only have one account right now, don’t overthink this. Tax location is an optimization that matters more as the portfolio grows. Put everything in the one account you have, in your target allocation, and add the tax location refinement later.
4. Know What You Do Not Do
The three-fund portfolio requires almost no active management. Its hardest discipline is staying out of your own way.
You do not sell because the market dropped. This is the single most important rule. Every market decline has eventually reversed. Every investor who sold during a decline and waited to “reinvest at the bottom” got the timing wrong — because no one can identify the bottom until it has already passed.
You do not check the portfolio every day. Frequent monitoring leads to frequent second-guessing. Quarterly is fine. Annually is fine. The portfolio does not need your attention. It needs time.
You do not add more funds because something has been working. Your three funds already own every publicly traded company on earth. Adding a sector fund (technology, healthcare, energy) means overweighting that sector. That is a prediction about the future. This strategy is specifically designed to eliminate predictions.
You do not switch strategies when passive feels slow. There will be years when individual stocks you didn’t own tripled. There will be years when an asset class you hold loses 20%. Both happen. Neither is a reason to abandon the plan.
The “You’re Done” Moment
At some point in this process — after the account is open, the initial purchases are made, and the automatic contributions are running — you will look at the setup and think: is this really it?
Yes. It is.
You have now built a portfolio that:
- Owns every significant publicly traded company in the United States and the world
- Holds bonds proportioned to your actual time horizon and risk tolerance
- Contributes automatically every month, rain or shine
- Rebalances once a year in a single session
That is the complete system. Two hours of setup, one session per year, nothing in between.
The Bogle approach is boring by design. Jack Bogle spent his entire career making the case that boring — consistent, low-cost, automatic — is better than exciting, and the data backs him up. Most investors who attempt something more sophisticated end up with lower returns, more taxes, and more stress than the boring version produces.
The interesting thing to work on, if you want to engage with your own finances, is understanding the businesses underneath the funds — what’s in the index, why the economy grows, what earnings cycles look like. That’s a different project from managing the portfolio. The portfolio, once built, largely manages itself.
A Note to Luca and Lili
There will come a moment where this feels too simple.
You’ll watch a friend describe an investing strategy that’s more complex, or hear about someone who tripled their money picking individual stocks, or see a fund advertised with a three-year track record that’s significantly better than the market.
All of those things will happen. And every time they do, I want you to come back to this:
The three-fund portfolio has one job: to let you participate in the growth of the global economy at the lowest possible cost, with the minimum of decisions. It doesn’t try to be the best-performing strategy in any given year. It tries to be a strategy you can hold for 40 years without making a catastrophic mistake.
That boring persistence, compounded over decades, beats most sophisticated alternatives.
Your job, once this is set up, is almost entirely psychological. Don’t panic when markets fall. Don’t chase when markets are rising. Keep contributing, month after month, regardless.
Time is on your side. Let it work.
— Papa
The One-Sentence Summary
Building your first portfolio means setting a stock-to-bond allocation matched to your life stage, putting three low-cost index funds in those proportions, automating a monthly contribution, rebalancing annually when any fund drifts more than five points from its target, and then — mostly — leaving it alone.
This is Part 3 of the Getting Started series. For a deeper look at why this approach works and how the three-fund portfolio has performed over real decades of data, see the Bogle Method series — which covers the full argument for low-cost index investing from first principles:
Getting Started — series overview
— Jim