How Does the Cost of an Attack Compare to the Potential Profit from a Double-Spend?

For a 51% attack to be economically rational, the potential profit from the double-spend must significantly outweigh the cost of acquiring the necessary hashrate and the risk of the coin's value collapsing. The cost includes the hashrate rental fees, energy costs, and the opportunity cost of not mining a profitable coin.

The profit is typically derived from the value of the assets acquired on an exchange before the double-spend is revealed. Smaller coins are targeted because their lower security cost makes the profit-to-cost ratio more favorable for an attacker.