that depends on how the weight is lost. there are healthy ways to lose weight and unhealthy ways. see how to lose weight safely. in general safe weight loss is about 1-2 pounds per week. the first month is more is typically lost due to fluid changes so 20 pounds in 2 months would probably be okay if it's done with a healthy diet. more rapid weight loss should always include monitoring from a doctor.
is it healthy to lose 20 pounds in almost 2 months but not quite 2 months?