This issue annual interest percent is equal to 100 multiplied by this issue AnnualInterest divided by this issue Debt.
For example if the estimated cost-to-fix the issue (this issue Debt) is equal to 10 man-days, and the estimated cost-to-not-fix the issue is equal to 2 man-days per year (this is this issue AnnualInterest) then the debt annual interest percent is 20% per year.
Notice that an annual interest percent higher than 100% means that during the next 12 monthes, it would be cheaper to fix the issue than not to fix it.
If this issue Debt is equal to NDepend.TechnicalDebt.Debt.Zero, this getter returns zero.

Reference

IIssue Interface
IIssue Members
AnnualInterestPercent(Debt,AnnualInterest) Method