If it's paid out as ordinary (W-2) income, then your top federal tax rate right this minute is 39.35% (37% regular tax, 1.45% medicare tax, 0.9% medicare surtax).

If it's paid out as some sort of investment income not subject to long-term capital gains treatment (e.g. interest, non-qualified dividends), then your top federal rate is 40.8% (37% regular, 3.8% net investment tax).

That does assume $500k of taxable income not counting the payout we're talking about here, to hit that 37% tax bracket.

If you have kids, you can hit these sorts of marginal rates at lower incomes too, because of the 5% marginal tax rate from the child credit phaseout.

I should note that money is fungible, so the fact that some of this is claimed to be "medicare" tax and some is claimed to be "income" tax is irrelevant to both the person paying the tax and the government collecting the tax. Medicare is not funded solely by the "medicare" tax in practice, so the fact that there's a separate tax is more or less an accounting oddity.