In most systems a gain is taxed when it is realised, not when it happens. That single rule means how often you trade changes your return even when every trade is correct.
11 min read · Level 4
Low turnover is usually defended as a tax strategy, and that undersells it. The tax arithmetic is real - 0.78 of a percentage point a year in the example above, compounded - but it is a consequence rather than a cause, and treating it as the cause leads people to hold bad things for tax reasons, which is the same error in the opposite direction. The better reading is that turnover is a measure of how often you believed you knew something, and the tax is simply the invoice attached to that belief. Every realisation says that the new holding is better than the old one by more than the bill, the spread, the commission and the chance of being wrong - and most of the time nobody has checked whether it is. What makes the tax point worth teaching is not that tax is expensive. It is that tax is the only one of those four costs that produces a document, in a fixed amount, with your name on it. It makes the price of activity legible, which is a service, and an investor who reduces turnover because the invoice made the price visible has arrived at the right behaviour by a slightly wrong route - which is still better than not arriving.
A taxable event is the moment a tax system decides something has happened. In most systems a sale is one; an increase in value while you still hold the asset is not.
Portfolio turnover is the proportion of a portfolio that is bought and sold in a year. A turnover of zero means nothing was sold. A turnover of one means, roughly, that the whole portfolio changed hands.
Put those together and you get tax drag: the reduction in compounding caused by paying tax earlier than you had to. It is the same shape as fee drag, and it has the same cause. Money that leaves stops compounding, and the loss is not the payment - it is the payment plus everything the payment would have earned for the rest of the hold.
The difference from fee drag is that this one is largely under your control, and that tax deferral is not tax avoidance. The bill still arrives. What deferral buys is the use of the money in the meantime, and the ability to choose the year in which the bill falls.
Jurisdictions differ on all of this - on what counts as a realisation, on whether losses can be set against gains, and on whether any of it applies to you at all. The mechanism below is general; the rules are not.
Because it puts a price on activity, and activity is the thing an investor finds hardest to resist.
Every argument for trading more - a better idea has come along, this one has run far enough, the position has grown too large - is answered in pre-tax terms, and the tax is the part that does not appear in the argument. A switch that improves the expected return by half a point and triggers a bill is not obviously an improvement, and nobody computes it in the moment.
And because it explains a result that otherwise looks like magic: two portfolios holding broadly the same things, earning broadly the same gross return, ending years apart. The difference is not skill. It is who sold.
This is educational information, not tax or accounting advice. Rules differ by country and change — get advice from a qualified professional in your jurisdiction before acting.
Educational, not personalised financial advice. Nothing in the Investor Academy is a recommendation to buy, sell or hold anything — what is right for you depends on your own circumstances and the rules where you live.
Sources: U.S. IRS — official tax information; UK Government — Capital Gains Tax guidance; OECD — tax policy and statistics
Illustrative rate again, because the real one depends on where you live: suppose gains are taxed at 25%, with no allowance and no other complication.
Starting amount: 10,000 Gross return: 7.00% a year Horizon: 25 years
Two paths. In the first, nothing is sold until the end, and the whole gain is taxed once at 25%. In the second, the entire gain is realised and taxed every year - the extreme case of full turnover.
Deferred to the end 10,000 x 1.07^25 = 54,274.33 gain 44,274.33, taxed at 25% = 11,068.58 left with = 43,205.74
Taxed every year net annual rate 7.00% x 0.75 = 5.25% 10,000 x 1.0525^25 = 35,937.89
The difference is 43,205.74 - 35,937.89 = 7,267.85, which is 16.82% of the deferred result. Both paths earned exactly 7.00% a year gross and both paid exactly 25% on every unit of gain. Nothing was avoided. The whole difference is when the money left.
Said as a rate: the deferred path produced an after-tax compound rate of 6.03% a year over the twenty-five years, against 5.25% for the taxed-annually path. That 0.78 of a percentage point is what timing alone was worth.
Real portfolios sit between these two extremes rather than at either end, and the point is the direction, not the magnitude: every realisation moves you from the first number toward the second.
Two things this example deliberately leaves out, because both cut the other way. A loss, where the rules allow it, can be set against a gain and reduce the bill in the year it is taken - which is a reason to sell something, not a reason not to. And a 25-year deferral assumes a rate in year 25 that nobody can know, so the deferred path carries a rule-change risk the annual path has already paid off.
The specific wrong move is rebalancing or switching a taxable holding without pricing the bill it triggers.
The reasoning that leads there is entirely sound up to the last step. The allocation has drifted, the discipline says return it to plan, and the discipline is correct - but in a taxable account the trade has a price, and a drift of a few percentage points may not be worth it while the same drift inside a sheltered account plainly is. The same rule produces different answers in different containers, and treating it as one rule is the error.
It is tempting because the tax appears months later, on a form, detached from the trade that caused it. Nothing at the moment of selling shows the cost, so the decision is made on a screen where the price is invisible.
The opposite error is real too, and worth naming: refusing to sell something that should be sold because of the tax. A position that has become too large, or a thesis that has broken, costs more to hold than the bill costs to pay. Deferral is worth a fraction of a gain; a permanent loss takes the lot.
Proceeds minus cost basis, times the rate that applies to you. One line, thirty seconds, and it converts an invisible cost into a number that can sit beside whatever the trade was supposed to gain.
Directing contributions and any dividends or interest toward the underweight holding moves the allocation back toward plan without selling anything. It is slower than selling, and it triggers nothing.
Where you hold both kinds of account, the same rebalancing is free in one and priced in the other. Put the activity where it costs nothing and leave the taxable account as undisturbed as its allocation allows.
Many systems allow this, with conditions - and several have rules that disallow the loss if a substantially identical asset is repurchased too soon. The conditions are specific, they differ by country, and getting them wrong removes the benefit entirely, so confirm them locally before acting.
Before any sale in a taxable account, when setting a rebalancing rule, and when comparing two funds whose strategies differ in how much they trade.
Do not let deferral keep you in a holding whose reason for existing has gone. And do not apply any of this to an account where gains are not taxed on realisation - inside such a wrapper the entire calculation is absent, which is precisely what makes it the right place to trade.
In some jurisdictions a fund that sells holdings inside the portfolio can pass the resulting gains through to its investors, who then owe tax on them without having sold anything themselves. It is entirely possible for an investor to receive such a distribution in a year when the fund's own value fell, because the realisations and the year's performance are separate things. Whether this happens at all, and in what form, depends on how funds are taxed where the investor lives.
For a fund held in a taxable account, find out whether its internal trading can create a tax liability for you, and treat a high-turnover strategy in a taxable container as carrying a cost that does not appear in its expense ratio.
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