As long as you stick to the plan, the minimum amounts are as follows:

 

10-year duration: Guaranteed to not be lower than 100% of the amount you invest over those 10 years

15-year duration: Guaranteed to not be lower than 140% of the amount you invest over those 15 years

20-year duration: Guaranteed to not be lower than 160% of the amount you invest over those 20 years