Calculation. Summary: This is the calculation used for figuring the yield to maturity of bonds and coupons purchased after 7/1/82 and before 1985 as described in example 21. The calculation is: ($100,000 divided by $20,000) raised to (1 divided by 25) power minus 1 equals (1.06649 minus 1) equals 0.06649 equals 6.649%.