Recuring wage types

Can someone help me to configure a wage type for recoveries in infotype 14 to default the end date of the recovery period once an input i s made for that wage type from the front end specifying the start date.I have specific recovery periods for each wage type like 3 months , 6 months etc and the client wants it to default instead of putting both the start and end dates manually. They want to only put the start date and the system defaults the end date.