Number of years from the annuity start date that annuity payment is guaranteed. This is called the "certain period."
If you enter any number of years greater than 0 in this field, the survivor will only inherit the annuity payment for the remaining years in the certain period if the annuitant dies before the period ends.
Furthermore, if you enter a certain period greater than 0 and if Lifetime Payments is set to NO, then not only will the survivor's payments be limited to the certain period, the annuitant's payments will also be limited to those years.
For a user that is single:
Since there is no survivor in the plan, setting Lifetime Payments to YES and entering a certain period greater than 0 is not allowed. No payment is shown. If the single user wishes to limit the payment to a set of years, the certain period can be entered to limit the years but the Lifetime Payments needs to be set to NO.