President Joe Biden has consistently pledged not to raise taxes on households making less than $400,000 a year.

Whether his tax proposal keeps or breaks that promise depends on one’s frame of reference.

Primarily, it’s a question of how an observer considers a taxpayer earning less than $400,000 who has a one-time income windfall, according to tax experts.

That might be from the sale of a home, business, stock or other asset — whether during life or at death — that has appreciated significantly in value.

Let’s consider a hypothetical family that consistently earns $200,000 a year over two decades:

Taxes likely wouldn’t rise for this household over that time, all else being equal, if Biden’s plan were enacted, experts said. However, the following year, the same family sells a highly appreciated business for $2 million. This would likely trigger a higher tax rate on capital gains that year, per Biden’s proposal.

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This scenario raises a fundamental question: Should the public consider such a taxpayer to fall in the category of people making less or more than $400,000?

Per a strict reading of Biden’s pledge, higher taxes for this hypothetical family (during the year of the business sale) wouldn’t break the president’s promise, according to tax experts. The family’s total income for the year would be $2.2 million — much higher than the $400,000 mark.

This is the lens through which the White House views Biden’s tax plan.

“Consistent with the president’s campaign proposal, individuals and families earning less than $400,000 will not see an increase in their taxes,” according to a White House official.

However, some observers might view higher taxes for this hypothetical family as breaking the “spirit” of the pledge, said Jeffrey Levine, chief planning officer at Buckingham Wealth Partners in Garden City, New York.

Such taxpayers had consistently earned less than $400,000 and spent years building up business equity, said Levine, an accountant and certified financial planner. The sale proceeds may be the family’s biggest source of retirement savings, too, he said.

Of course, Levine said, this scenario wouldn’t be a technical breach of Biden’s campaign pledge and would only apply to a tiny fraction of taxpayers.

“So many of the changes [the administration is] talking about, they’re all geared toward those who make more than $400,000,” he said. “They’ve done a solid job of holding to that campaign promise.”

Biden’s tax proposal would likely affect aforementioned taxpayers via a higher capital gains tax, which is paid on an asset’s appreciated value.

The Biden administration aims to raise taxes on the wealthy to fund domestic initiatives, like additional years of free education and expanded tax credits, in the American Families Plan. The benefits would largely accrue to low- and middle-income households.

The president would raise the top capital-gains rate to 39.6%, from the current 20%, for assets sold after more than a year of ownership. (That would be the same top tax rate as regular income.)

It would only apply to taxpayers whose adjusted gross income exceeds $1 million — the top 0.3% of taxpayers.

And only the portion of income or gains over $1 million would be taxed at the top 39.6% rate, according to a White House official.

The administration would also change rules around how assets are treated at a taxpayer’s death.

Specifically, death would be treated as a “realization” event. Assets with more than $1 million of appreciation would be treated as if sold — and subject to capital gains tax. (It would apply to married couples with at least $2 million of gains.)

Currently, appreciated assets aren’t subject to a capital gains tax at death. Heirs receive stock, homes and other assets at current market value and only pay tax on subsequent gains if and when they sell.

The first $1 million for single taxpayers ($2 million for married couples) would be excluded from Biden’s tax on unrealized capital gains. Single and married taxpayers could exclude an additional $250,000 and $500,000 of gains, respectively, for a principal residence.

There are limited scenarios in which taxing unrealized gains at death would affect taxpayers who’d earned less than $400,000 the year they died, according to Howard Gleckman, a senior fellow at the Urban-Brookings Tax Policy Center.

For example, this might apply to an individual who bought a lot of Microsoft stock in the 1980s and held it until death, but had been living on a modest Social Security and pension income, according to Gleckman.

“That’s the guy who’d fall between the cracks and end up paying the tax even though he was making less than $400,000 in that last year of life,” he said.

These situations would apply to just 0.6% of taxpayers earning between $200,000 and $500,000 the year they died, according to a Tax Policy Center analysis.

“We’re talking about relatively few people,” Gleckman said. “But it’s not zero.”

Of course, such taxpayers would be deceased; higher taxes may not much matter in these cases, from a practical perspective. But they’d perhaps leave a smaller estate for heirs, to the extent assets had to be sold to pay for the additional tax. (There are mechanisms like insurance to prevent such an outcome, however.)

And the Biden administration offers certain exemptions to blunt the impact of a capital gains tax at death. For example, certain family owned and family operated businesses wouldn’t owe tax until the business ceases to be family owned.