Simple Interest Monthly Payment Tables Author:Financial Publishing Company Calculate your monthly payments quickly and accurately. Precomputed Operations. Rates from 4% to 25%, mostly in 1/4% steps. Terms from 6 to 48 mos by 6 mos; 60 to 120 months by 12 mos; 144 and 180 months. Dollar amounts to $25,000 and OK to combine lines for additional amounts.