 In 1964, the effective capital gains tax rate was 25%.This means that the actual tax percentage of all capital gains realized in the U.S. in 1964 was 25% as opposed to the nominal capital gains tax rate, or the percentage that would have been collected by the government prior to deductions and evasions.This effective rate held constant until a small rise in 1968 up to 26.9% and then began steadily increasing until it peaked at 39.875% in 1978.