How is the monthly payment calculated in a debt reduction program?

Are you referring to a debt management plan or to a settlement company? With a debt management plan, your payments will probably be about the same as what you are currently paying for minimums, give or take a bit. However, you will probably get lower interest rates, and therefore pay your balances off sooner. With a settlement company, it depends how long the program is for and what percentages the settlement company thinks they can settle for, plus what their fees are.