Personal Finance (25): Is Your Trading System Really Good Enough To Trade Full-Time? (2/3)

 Advertising presents full-time trading as a natural replacement for a job: quit the office, free from traffic jams, trade from anywhere, be free by Friday, and the list goes on.

In a bull market the pitch is convincing: when almost everything is rising, almost everyone looks like a genius. Then the market changes. And the large majority of those who took that path fail badly.

This article works through the arithmetic behind the sales pitch, in two steps.

Step one was established in Part 1 (the last article). Professional fund managers — full-time, credentialed, with research teams and direct market access — rarely beat a simple S&P 500 index fund over ten to twenty years. Across fifteen years, roughly nine out of ten active US large-cap funds underperformed it. If that is the record of full-time professionals, the promise made to a beginner deserves real skepticism.

Step two is this article’s subject. Suppose you are the exception, and genuinely hold something better: a long-only system returning 16% a year, with a 25% maximum drawdown and no leverage. Better than the index; better than most professional funds ever achieve. Surely that is enough to quit?

Given a genuinely good system, what capital — and what conditions — must actually be in place before you can live from it?

The intuitive answer is to divide the income you need by 16%. In the stress test that follows, the honest answer is three to four times larger.

That gap is not a technicality. A system’s average return tells you how wealthy you might eventually become; its drawdown decides whether you survive long enough to find out.

None of this is an argument against trading. It is an argument against quitting before the numbers support it.

0.  Setting Up the Exercise

This exercise answers a concrete question: with a genuinely good long-only system (16% CAGR, 25% max drawdown), how much money does an ordinary senior engineer need before he can responsibly stop working — and how many years of saving does it take to get there, starting from nothing?

All figures are rounded, US-based, and built on the assumptions below. They are illustrative, not advice; change any input and the answer changes. This version corrects an important omission flagged in review: a salaried job pays far more than its cash salary once employer benefits are counted — and quitting means self-funding all of them.

0.1  A critical caveat on “long-only, 25% drawdown”

The whole model assumes the system’s worst loss is 25%. For a long-only system that only holds true if it has a trend or cash-conversion filter that moves it to cash when the broad market breaks down. Without such a rule, a long-only system in a secular bear market (2000–03, 2008, or 1973–74) does not politely stop at −25% — it can draw down far deeper and stay there for years, because it has no way to profit from or side-step the decline. Every number in this paper depends on that filter working. A “16% / 25%” system with no exit to cash is a different, more dangerous animal than the one modelled here.

1.  Scenario 1 — Quit Now, Trade Full-Time

The question: what lump sum lets him quit today and live off the system, keeping the same standard of living — including the benefits he used to get for free?

1.1  The naive answer (and why it’s a trap)

His real cost to replace is ~$105,900 (take-home + self-funded benefits). To net that after ~28% short-term tax, he must earn about $147,000 gross in trading profit. The tempting math is:

$147,000 ÷ 16% = $919,000.

This is dangerously wrong. It assumes he earns exactly 16% every single year. He won’t — and the years he doesn’t are the years he still has to eat and pay for his own insurance.

1.2  The stress test that breaks the naive number

Run the exact worst case: he quits, immediately hits the 25% drawdown, and the market goes flat for 3 years while he keeps withdrawing $147k/year to live.

Fig. 1 — Same shock, three starting capitals (benefits-adjusted). At $0.92M the account is gutted with no job to return to; at ~$2.94M it endures.

1.3  The honest answer

The Most Dangerous Moment

The riskiest point is not when someone has no experience. It is when they have just enough success to feel certain.

It usually unfolds in five stages.

Stage 1 — A bull market. They start trading, and the account performs well. Almost everything is rising, so almost everyone looks skilled.

Stage 2 — Confidence. The thought arrives: “Why am I working for someone else when I can make more than my salary doing this?”

Stage 3 — The salary becomes the enemy. The job stops looking like the thing financing the experiment and starts looking like the obstacle to it.

Stage 4 — Resignation. They quit — usually near the top of their confidence, which tends to coincide with the top of the market.

Stage 5 — Trading changes character. This is the critical shift.

Before quitting, the question was: “Let’s see what my system can do.” After quitting, it becomes: “This month’s trading has to pay my bills.”

Those are two entirely different psychological and financial situations — and the system does not know which one it is in.

2.  Scenarios 2 — Keep the Job, Drip-Feed the System

This is the realistic path, and the good news. Running a finished weekly-rebalanced system takes little daily time — easily compatible with a full-time job. (Developing and validating a robust system is another matter entirely, and Part 3 is devoted to it.) So instead of quitting, he keeps his salary and its benefits, invests a fixed slice of his net take-home into the system every year, and lets it compound at 16% until it reaches the ~$2.94M “quit” milestone. Then he can leave — and, if he likes, travel the world while the system runs from a laptop.

To keep it simple and conservative, we assume no salary increases ever (real raises would speed everything up), and that contributions are made once a year and compound at the system’s 16%. Because he keeps his job, his benefits are still covered while he accumulates — another reason the drip-feed path is so much safer than quitting.

2.1  How many years until he can quit?

---------------------  Work on Progress - to be continued  in the next two days  -------------------