After-tax asset allocation: why your 60/40 might really be a 55/45

Here's a question almost nobody asks: when you say you have a 60/40 portfolio, whose money are you counting? A dollar in a Roth IRA is fully yours. A dollar in a traditional 401(k) is yours minus whatever tax rate applies when you withdraw it — the IRS holds a silent lien on every pre-tax account. Once you accept that, a strange conclusion follows: your true, spendable asset allocation differs from the one on your statement, sometimes by enough to change decisions. This is after-tax asset allocation — a genuinely advanced idea that's mostly ignored, occasionally overapplied, and worth understanding either way.

The core insight: the IRS owns a slice of your traditional accounts

If you expect to withdraw from a traditional IRA at an effective 22% rate, then only 78 cents of each pre-tax dollar is yours. Economically, it's as if you own 78% of the account and hold the other 22% on the government's behalf — including the government's share of all future gains and losses. Your Roth accounts are 100% yours. Taxable accounts sit in between: you own the basis outright, but embedded gains carry a future capital-gains haircut of 15-20% on the gain portion.

Why this interacts with asset location

Standard asset-location advice says put bonds and other tax-inefficient assets in traditional accounts and stocks in Roth and taxable. Follow it, and the after-tax effect systematically pushes your true allocation more aggressive than your statement: the government absorbs a share of the (bond-heavy) traditional account, while your fully-owned Roth holds the high-growth assets. That's not a flaw — the Roth holding stocks is precisely why asset location adds value, since you keep 100% of the highest expected growth. But it means investors who carefully located assets and then set allocation targets on pre-tax values are running hotter than they think, usually by 2-6 percentage points of equity.

Choosing the discount rate is the hard part

The whole calculation hinges on your expected effective tax rate in withdrawal — which is uncertain over decades. Use your best estimate of the average rate on future withdrawals: for most retirees that's well below their working marginal rate, because withdrawals fill the standard deduction and lower brackets first. A common, defensible choice is 12-22%. Two honest warnings: RMDs can push large traditional balances into higher brackets than you planned, and tax law itself drifts. Precision is impossible; the point is that 0% — the implicit assumption of ignoring the issue — is the one estimate guaranteed to be wrong.

When it actually changes decisions

• Large traditional balances with aggressive asset location: the gap between stated and true allocation is biggest here — worth computing once.
• Roth conversion analysis: converting doesn't change your after-tax wealth today (at a constant tax rate), but it does change your true allocation — a converted dollar of stock becomes fully yours, effectively increasing your real equity exposure without a trade.
• Setting withdrawal-phase risk: retirees living on the portfolio should size their true bond floor in after-tax dollars; a '5 years of spending in bonds' cushion held pre-tax is really 4 years.
• Comparing your progress to a retirement number: a $1M target met with $1M of traditional money is 12-25% short in spendable terms.

A once-a-year procedure

1. List each account with its balance and asset mix.
2. Pick an expected effective withdrawal tax rate for traditional accounts (say 20%) and a capital-gains haircut for taxable embedded gains (say 15% of the gain).
3. Multiply each account's assets by your true-share percentage and re-sum stocks and bonds.
4. Compare the after-tax allocation to your target. If it's more than ~5 points off, adjust — preferably by re-locating future contributions rather than selling.
5. Note the number in your investment policy statement so next year's check takes five minutes.

The bottom line

Your account statements report dollars; your retirement will be lived on after-tax dollars, and the two diverge by exactly the government's embedded share. Discounting traditional accounts by your expected withdrawal tax rate reveals your true allocation — usually a few points more aggressive than stated if you've located assets well, and your true net worth — usually 10-20% smaller than the statement total. Run the arithmetic once a year, size your retirement number and bond floor in spendable dollars, and then put the spreadsheet away. The goal isn't tax clairvoyance; it's simply refusing to count the IRS's money as your own.