my wifes ex owes her $50,000 for child support.whats a good $ for lumpsum payoff?

It doesn't matter what a good lump sum pay off is. First, if the child support is being paid through the Court System, they determine what is owed + interest. And if an ex is ordered to pay through the Courts, and decides to make a lump sum payment directly to his ex? It's seen as a gift by the courts.

$50,000 sounds fair. Are you seriously proposing LOWERING the amount this guy owes to reward him for being late with his payments? Most places, if you borrow money, they make you pay back MORE than you've borrowed to cover interest. The way I see it, this guy has been borrowing money from his kids for a long time, and he should be paying back every last cent, at the very least.

The ex wife CAN NOT determine this. The money is not HERS. It is owed to the children. Only a court could decide IF a settlement could be made for less.

Since when do they do this for C.S. payments? How did this deal get made?

$60,000 including interest for being a bum

$50,000.

Otherwise he makes payments.