We need the advice of a qualified actuary using the projected unit method.
Graduating at Harvard in 1825, he was a teacher till 1835, was an actuary in 1835-1845, and then became assistant at the Washington observatory.
The yearly rate is calculated by the SSA Chief Actuary, and is available on the agency's website.
Insurance companies like Cigna are constantly recruiting new actuaries, and an experienced actuary may actually find recruiters from other companies attempting to woo them away from their current employer.
Appointed in 1862 actuary to the United States sanitary commission, he issued in 1869 an important volume of Military and Anthropological Statistics.