The 70/30 Rule for Single-Stock Concentration: An Anchor, Not a Formula

The 30% single-stock cap shows up in almost every wealth-management conversation with tech employees. A senior IC at a public tech company hears it from two advisors and assumes it must be a regulation or a tax rule. It is neither. It is a heuristic, a rough anchor point that advisors use to frame the diversification conversation.

That does not mean it is arbitrary. The 30% number comes from risk-decomposition analyses showing that, past roughly 30% of a portfolio in one stock, the portfolio’s standard deviation is materially higher than what a diversified portfolio produces, and the marginal benefit of further concentration (expected return) is typically not enough to compensate for the extra risk.

But it is an anchor, not a formula. A holder with $2M net worth and $1.4M in one stock (70% concentrated) faces a very different calculus than a holder with $50M net worth and $35M in one stock. Both are at 70% concentration, but the second holder has $15M of diversified backup and can afford the risk the first holder cannot.

Where the number comes from

Empirical studies of single-stock risk show concentrated portfolio volatility approximately doubles at 25-30% concentration vs a diversified equity portfolio. Past that level, portfolio risk is dominated by the single-stock exposure and looks more like holding a single stock than holding a diversified portfolio with one large position.

Moynihan and Hakansson (Journal of Portfolio Management, 2001) and similar studies also examined the probability of “catastrophic” drawdowns (a single stock losing 50%+ in a year) and showed that a 30%+ concentration in a single stock typically produces drawdown patterns that would destroy a year or more of median diversified portfolio returns in a bad outcome.

The 30% anchor is conservative. More rigorous frameworks use different cutoffs depending on the stock’s volatility, the holder’s age, and outside income sources.

When 30% is too conservative

Some holders can tolerate more than 30% concentration without impairing their plan:

• Young holders with 30+ years of human capital and high income elasticity. A bad outcome on the stock is absorbed by future earnings.
• Holders with large outside diversified assets. A $20M diversified portfolio plus $10M in employer stock is 33% concentrated, but the $20M is a meaningful safety net.
• Holders in low-cost-of-living regions with moderate spending. Spending $200K per year against a $10M diversified buffer means the concentrated position could go to zero without impairing the lifestyle.
• Holders who hold concentrated positions for tax reasons approaching a known event (QSBS maturation, step-up at death, charitable gift).

For these profiles, 40-50% concentration can be acceptable if the downside case is survivable.

When 30% is too aggressive

Other profiles cannot tolerate even 30%:

• Holders whose liquid net worth is mostly in employer stock and whose primary income is from the same employer. The stock and the paycheck are correlated. If the company stumbles, both stop.
• Holders nearing retirement without pension or social-security replacement for their spending. A 30% concentration at age 62 is more risky than the same concentration at age 32.
• Holders with illiquid real estate, private business interests, or other non-publicly-valued assets. Apparent diversification may be concentration in disguise.
• Holders with large fixed liabilities (mortgage, college tuition commitments) against limited backup.

For these profiles, 10-20% concentration is the prudent target, with more aggressive diversification timelines.

Using the anchor correctly

The 30% number is useful as a starting point for conversation, not as a strict limit. Correct use:

1. Calculate the holder’s true net worth, including home equity, retirement accounts, and illiquid positions.
2. Identify the portion of that net worth that is effectively in the employer company (stock, unvested equity, and future expected comp from the same employer).
3. Compare to 30% as a rough check. If above 30%, start asking why and what the plan is to reduce.
4. Pressure-test at 50% drawdown. If the stock loses half, is the holder’s plan still viable?

A 28% concentration that fails the drawdown test is worse than a 45% concentration that passes it. Concentration percentage is correlated with risk but not identical to it.

Comparison: reasonable thresholds by situation

These are defaults. Individual situations override.

The glide-path approach

Rather than a one-time reset from 60% to 30%, many holders move along a glide path: take concentration from 60% to 50% over year one, 50% to 40% over year two, 40% to 30% by year three. This has several advantages:

• Spreads the tax hit across multiple years for better bracket management.
• Allows time to harvest losses in a direct-indexing overlay to offset gains.
• Gives the holder time to emotionally adjust to the reduced concentration.
• Creates optionality if the stock rallies (less sold at lower prices) or falls (hedging can be added at lower cost).

The glide-path target should be written down, with annual checkpoints. Discipline on the schedule is more important than the precise exit pace. Drift can be the worst outcome: planning to diversify, not actually executing, and then watching a drawdown take away the option.

Tax-efficient tools for reducing concentration

Once the target concentration is defined, the tools to move there include:

• Staged selling across tax years.
• Exchange funds for deferred diversification.
• Direct indexing to harvest offsetting losses.
• Charitable gifting of appreciated shares.
• CRT for diversification plus charitable exit.
• Collars and VPFs for hedged positions without sales.
• 10b5-1 plans for executives who cannot trade during windows.

Each tool has its own article in this series. The core discipline is setting a target and working toward it, not choosing the perfect tool before taking any action.

Frequently asked

Is the 30% limit in any tax or securities regulation? No. It is a planning heuristic. No IRC or SEC rule enforces it.

Does “concentration” mean market value or cost basis? Market value. A $3M position with $100K basis contributes $3M to concentration, not $100K. The risk is based on current value.

Should unvested RSUs count? Yes, to a degree. Unvested RSUs tied to the same employer contribute to concentration because they will vest and add to the exposure. They are “concentrated” future income, not diversified.

What about ESPP shares? Same logic: they are employer stock and count toward concentration. Selling ESPP shares promptly (after any qualifying disposition period) is often the right move for diversification purposes.

Is it different for private-company stock? The concentration problem is worse for private-company stock because exit timing and pricing are uncertain. A 40% private-company concentration is meaningfully riskier than a 40% public-stock concentration.

Next step

Do the math today. Add up all employer-related exposures (stock, RSUs vesting in the next 3 years, ESPP, options). Add them to your overall investable assets (include 401(k), IRA, taxable accounts, emergency fund). Compute the employer share as a percentage. If you are above the anchor for your profile, set a written glide path with annual targets and pick one reduction tool to start executing this quarter.