Unrealized Gains: The Paper Profit That Comes With a Hidden Tax Bill Attached
Watching a portfolio balance climb feels a great deal like winning, but that number can shrink or vanish just as quickly as it appeared, and even converting it to cash costs something. An unrealized gain is the increase in value of something you still own, and it stays a number on a statement, not spendable wealth, until the day you actually sell.
The core principle
An unrealized gain is the increase in an asset's value while you still own it, calculated as current market value minus cost basis:
unrealized gain = current market value − cost basis
It becomes a realized gain, and a taxable event in most account types, only at the moment you actually sell. Until then, the gain exists entirely on paper: it can shrink, vanish, or grow further before you act, and in a taxable brokerage account, no capital gains tax is owed on it while it remains unrealized, regardless of how large it grows or how long you hold it.
This distinction matters more than it first appears, because an unrealized gain is not equivalent to cash in the way a bank balance is. Selling to access that value triggers a tax bill sized to your holding period and marginal rate, which means the actual, spendable value of an unrealized gain is meaningfully less than its face amount the moment you plan to realize it. Two investors with identical account balances can have very different real net worth if one holds mostly cost basis and the other holds mostly unrealized gain, because the second investor is carrying an embedded, unpaid tax liability the account statement does not show.
US tax law also contains a provision that interacts directly with unrealized gains at death, called step-up in basis: an inherited asset's cost basis resets to its fair market value on the date of the original owner's death, which means an unrealized gain that was never sold during the owner's lifetime can pass to heirs and disappear from a tax standpoint entirely, never taxed at all under current law.
Inside tax-advantaged accounts, the entire concept behaves differently. A traditional 401(k) or IRA defers tax on gains regardless of whether they are realized or unrealized, so trading and rebalancing inside the account triggers no current tax event either way, and a Roth account goes further, since qualifying withdrawals of both contributions and all accumulated gains, realized or not, are never taxed at all. The unrealized-versus-realized distinction that matters so much in a taxable brokerage account is functionally irrelevant inside these wrappers, which is part of why financial planners generally recommend holding actively traded or high-turnover strategies inside tax-advantaged accounts rather than taxable ones.
How the math works
Example 1: calculating the gain and the tax cost of realizing it. An investor bought 200 shares at $45 each, for a cost basis of 200 × $45 = $9,000. The shares now trade at $78, for a current market value of 200 × $78 = $15,600. The unrealized gain is $15,600 − $9,000 = $6,600, a 73.3% unrealized return on the original investment. If the investor sells today, having held the shares over a year, the gain qualifies for long-term capital gains treatment. Assuming a 15% federal long-term rate plus the 3.8% net investment income tax for a total of 18.8%, the tax owed is $6,600 × 0.188 = $1,240.80, leaving after-tax proceeds of $15,600 − $1,240.80 = $14,359.20. The $6,600 headline gain, in other words, is really worth about $5,359 after tax, not the full $6,600.
Example 2: the same position never sold, passed to an heir. Suppose instead the investor holds those same shares until death, still worth $78 each with the same $6,600 unrealized gain never realized during their lifetime. Under step-up in basis, the heir's new cost basis becomes $78 per share, the fair market value on the date of death, not the original $45. If the heir sells immediately at $78, the taxable gain is $15,600 − $15,600 = $0, meaning the entire $6,600 gain that had built up over the original owner's lifetime is never subject to capital gains tax at all, a permanent difference of $1,240.80 in tax compared to Example 1, purely as a function of when and by whom the asset was sold.
How it shows up in real portfolios
The most common real-world friction shows up in concentrated positions built up gradually through employer equity compensation. An employee who has received restricted stock and stock options over many years at a company whose share price has climbed steadily can end up with a large single-stock position where most of the value is unrealized gain, not original contribution, which makes diversifying feel expensive even when the concentration risk has grown to dominate the portfolio.
A useful high-earning-professional scenario: a hospital system physician who participated in an old employer's 401(k) brokerage window years ago holds a legacy position now worth $250,000, of which $200,000 is unrealized gain on an original $50,000 basis. Rebalancing that position into a diversified portfolio would trigger a substantial capital gains tax bill, and the physician keeps deferring the decision year after year, even as the position grows to represent a larger and larger share of total net worth, a classic case of a real, understandable tax cost outweighed in importance by an even larger, underappreciated concentration risk.
Tax-loss harvesting decisions run directly through this same mechanic in the opposite direction: an investor selling a position with an unrealized loss elsewhere in the portfolio can use that realized loss to offset gains realized from trimming an overgrown, unrealized-gain-heavy position, reducing or eliminating the tax cost of finally rebalancing.
Charitable giving offers a specific and often underused way to unlock a large unrealized gain without ever paying the associated tax. Donating appreciated shares held more than a year directly to a qualified charity or donor-advised fund, rather than selling the shares and donating cash, lets the donor deduct the full fair market value of the shares while avoiding capital gains tax on the appreciation entirely, a combination that neither selling first nor giving cash can replicate on its own.
Estate planning and unrealized gains intersect directly through the step-up provision, which means a household with substantial unrealized gains sometimes benefits more from holding a position for life and letting it pass to heirs than from any lifetime tax-minimization strategy, a conclusion worth revisiting with a tax professional whenever a large embedded gain and an aging investor's time horizon come together in the same financial plan.
Actionable breakdown
- Track the gap between value and basis:
- Keep accurate cost basis records for every position.
- Check unrealized gain as a share of total position size.
- Before treating a gain as usable wealth:
- Estimate the after-tax value, not the headline number.
- Factor your actual marginal capital gains rate.
- Manage concentration risk deliberately:
- Weigh the tax cost of selling against the risk of not selling.
- Consider realized losses elsewhere to offset the tax bill.
Common pitfalls
- Treating unrealized gains as fully spendable net worth, then being caught off guard when a market decline erases a balance that was never locked in to begin with.
- Refusing to rebalance out of a winning position purely to avoid paying tax, even after it has grown into a dangerously outsized share of total wealth.
- Forgetting that a large unrealized gain represents a real, if deferred, future tax liability that should be accounted for in retirement and estate planning, not treated as a surprise later.
- Assuming step-up in basis applies inside retirement accounts, when IRAs and 401(k)s are already governed by entirely separate tax rules that step-up does not touch.
Related concepts
For what you are measuring the gain against, see cost basis. For the taxable event that finally converts a paper gain into cash, see capital gain. For the provision that can erase this gain entirely at death, see step-up in basis. For the technique used to offset the tax cost of realizing a gain, see tax loss harvesting, and for the risk a large unrealized position often masks, see concentration risk.
The bottom line
An unrealized gain is a real number worth tracking closely, but it is worth less than its face value the moment you plan to spend it, and worth potentially nothing in tax if you never sell at all.