91%

The top marginal tax rate in 1960 was 91%, which applied to income over $200,000 (for single filers) or $400,000 (for married filers) – thresholds which correspond to approximately $1.5 million and $3 million, respectively, in today’s dollars. Approximately 0.00235% of households had income taxed at the top rate.

https://taxfoundation.org/some-historical-tax-stats/#:~:text=(In%202008%2C%20the%20top%201,%2C%20respectively%2C%20in%20today's%20dollars.