I set an upper bound of 1 year maximum to be out of the field of programming. When I came back (should have kept programming while unemployed, stupid, I know) not only had my skill set deteriorated but so did my market rate. Out of college my salary was $98,000. By the time I had gotten back into the work force my salary was $65,000. It took about 1.5 years of hard work and a lot of overtime to get back to where I was. And during this time my peers that stayed employed have grown a lot both in terms skill set and market rate. So basically because I took 1 year off, I lost ~2.5-3 years of my career because I had to work back to where I was before.
I think if I were to get a do-over I would have not have taken a year off. But the grass is always greener on the other side of the fence, as they say.