Buy the Dip—But Only If You Have a Deployment System

Part 5 of the Rational Compounding Framework

March 2020. The S&P 500 drops 34% in 23 days. I watched three groups of people respond to the same event in completely different ways.

The first group panic-sold. Locked in losses. Spent the next 18 months watching the market double from the sidelines. The second group said “buy the dip” — on Twitter, in group chats, in conversations over video calls — and then did nothing, because they had no cash available to act on the advice they were giving. The third group had a system. They put $50K to $200K to work during the crash and captured one of the fastest recoveries in market history.

Group three didn’t win because they were smarter or calmer or had better information. They won because they’d built something in advance: dry powder and a set of mechanical rules for deploying it. That’s the whole secret. And it’s less common than you’d think.

Why Almost Nobody Actually Buys the Dip

The phrase “buy the dip” has been repeated so many times it’s lost all meaning. Everyone agrees with it in principle. Almost nobody is positioned to act on it when it matters.

The first problem is structural: most investors are fully deployed. A typical high earner has their 401k maxed and invested, their taxable brokerage fully in the market, and an emergency fund they won’t — and shouldn’t — touch. When the crash arrives, their deployable capital is zero. They’re spectators. You can’t buy the dip with money you don’t have.

The second problem is psychological, and it’s worse. Even investors who do have cash available tend to freeze. The market drops 10% and the question is whether this is the real dip or just the beginning. It drops 20% and the debate shifts to whether it’s heading to 30. At 30%, everything feels like a falling knife and the media is running comparisons to 2008. By the time clarity arrives — when it’s obvious in retrospect that the bottom was behind you — the recovery has already happened.

I’ve tracked this pattern through multiple cycles. The problem isn’t information or conviction. It’s that crashes feel different from the inside than they look on a chart afterward. In real time, they’re terrifying. CNN is running end-of-world coverage. Your portfolio is down $200K. Your friends are selling everything. Your gut is telling you this time is different. Without a system that removes thinking from the equation, most people either act too early, act too late, or don’t act at all. All three feel equally bad when you’re living through them.

The solution isn’t to become someone who doesn’t feel fear during crashes. It’s to build a system that doesn’t require you to act through it.

The 85-10-5 Model

The framework is simple enough to explain in one sentence: 85% of your portfolio is always invested, 10% sits in a high-yield savings account as an opportunity fund, and 5% is held as dry powder for severe crashes.

The 85% is your core portfolio — 401k, IRA, and the bulk of your taxable brokerage, invested in broad index funds and left alone. You contribute to it on schedule regardless of what markets are doing. This is where dollar-cost averaging during crashes does its quiet work — the regular contributions keep buying throughout the downturn without requiring any decision-making.

The 10% opportunity fund is where the model gets interesting. This money earns 4–5% sitting in a high-yield savings account, which feels like a sacrifice during bull markets. It isn’t. It’s insurance — insurance that has a specific, mechanical trigger for paying out. When the S&P drops 20% from its recent high, you begin deploying this fund in tranches: 25% at the -20% mark, another 25% at -25%, and the remaining 50% at -30%. You don’t decide based on how things feel. You follow the rules you wrote in advance.

The 5% dry powder reserve is for severe crashes — the 2008-level events that happen once every 15 to 20 years. It activates only when the market is down 30% or more, and at -40% you deploy everything remaining. This tranche has only been fully relevant twice in the past 50 years, but when it is relevant, having it available is the difference between observing history and participating in it.

Here’s what this looked like during the COVID crash. If you had a $1M portfolio in February 2020, your opportunity fund was $100K and your dry powder was $50K. When the market hit -20% on March 12th, you put $25K to work. When it hit -34% on March 23rd, you deployed the rest of the opportunity fund and half the dry powder — roughly $125K total, at an average S&P level around 2,400. By December 2020, the index had recovered to 3,700. That $125K was worth approximately $193K. Not because you timed the bottom — you didn’t — but because you had capital and rules when everyone around you had neither.

The data on why this works consistently isn’t complicated. Since 1950, a 10% market correction has happened roughly every 18 months. A 20% bear market arrives every four to five years. A 30% crash comes around every decade. These aren’t surprises. They’re scheduled opportunities for investors who are built to take them.

The Behavioral Insurance Argument

There’s an honest objection to this model, and it deserves a direct answer: mathematically, staying 100% invested beats the 85-10-5 approach over long periods. The market goes up in roughly 74% of years. Holding 10–15% in cash creates drag. On a spreadsheet with no behavioral errors, full investment wins.

The problem is that spreadsheets don’t feel fear.

When your $1M portfolio drops to $600K in six weeks, something happens to human decision-making. The rational investor who planned to hold through any drawdown discovers that planning to hold and actually holding are different things. The research on investor behavior consistently shows that individual investors underperform the funds they’re invested in — not because the funds are bad, but because investors buy after rises and sell after drops. The gap runs around 1.5% annually over long periods. On a $1M portfolio, that’s $15,000 a year in self-inflicted underperformance, compounding.

The 85-10-5 model is behavioral insurance. You accept a small cash drag — roughly 0.5–1% annually in foregone returns during bull markets — in exchange for something more valuable: a reason to be a buyer when everyone around you is selling. The opportunity fund gives crashes a different emotional valence. Instead of watching your wealth evaporate, you’re executing a plan you built when you were calm. That psychological shift is worth more than the spreadsheet math suggests.

This is also why the model works during slow drawdowns, not just sharp crashes. The 2022 decline ground lower over most of the year — the S&P dropped 25% peak to trough between January and October. If you deployed at -20%, you were underwater for months before the recovery. But the rules held, the recovery came, and the money made. The system doesn’t promise perfect timing. It promises you participate in recoveries, which have happened after every single drawdown in the history of the US market.

Building It Before the Next Crash

The setup is straightforward. Calculate 10% of your investable assets and move that amount — gradually, over 12 months if needed — into a high-yield savings account or Treasury money market fund. Do the same for the 5% dry powder reserve. Set price alerts on the S&P 500 at -20%, -25%, -30%, and -40% from its recent high. Write the deployment rules on paper and keep them somewhere visible.

When the alert triggers, you don’t think about whether now is the right time. You don’t check what the news is saying. You execute the rule you wrote when markets were calm and your judgment was clear. The wealth system works because decisions made in advance, in writing, are more reliable than decisions made in real time under stress. This is that principle applied to its most high-stakes moment.

Don’t build the opportunity fund by selling existing positions. Build it from savings over time, replenish it after using it, and keep it separated from your emergency fund — which has a different job and shouldn’t be touched.

What to buy when the triggers fire is simple: broad US market index funds. VTI, VTSAX, FZROX — whichever version your brokerage holds. Crashes are not the moment to pick sectors or individual stocks. They’re the moment to buy the market at a discount and wait for the recovery that has, without exception, always arrived.

I don’t know when the next one hits. Neither do you. But the crashes come on schedule — every few years, reliably, with full media coverage and maximum fear. The only question worth answering now is whether you’ll be a spectator or a buyer when it does.

Build the system before you need it. That’s the whole discipline.

This is Part 5 of the Rational Compounding Framework. Read Part 1: The Math of Wealth, Part 2: The 3 Engines, Part 3: Why High Earners Fail, Part 4: The RSU Trap, or see the complete framework.

Next in the series — Part 6: The Illusion of “Tax Hacks”