Jeff Bezos has an ex-wife, a girlfriend, four children and billions of reasons to watch whether U.S. President Joe Biden’s tax overhaul wins congressional approval.

The Amazon.com Inc. founder’s heirs may have to pay more than $36 billion if the president succeeds in closing a loophole that helps the rich transfer their fortunes tax-free at death.

Under current rules, whoever inherits the Amazon shares Bezos bought in 1994 for $10,000, worth $180 billion today, will receive a so-called step-up in basis, wiping out any capital gains tax liability. Biden’s plan would close that loophole and apply the top capital gains tax immediately when assets transfer to wealthy heirs. If the rate increases — it’s 20% for holdings such as Bezos’s, and Biden has called for boosting it to 39.6% — the eventual tax bill would too.