The answer to this question is pretty much the same as how a late payment is going to affect your credit score. It is impossible to predict accurately as to the impact a settled account is can do have on your credit score.
A debt settlement will typically have a negative impact on the credit rating of person. But the thing to consider is that a debt settlement happens on an account that is already delinquent. If the account has already been reported as delinquent, the negative impact on the credit rating has already occurred. One option that the consumer has during the debt settlement is to try and convince the creditor that he should report the account as paid and closed in exchange for setting the debt. Not many creditors might agree to do this but some may. If you can change the status of your account on the credit report from the link went to paid off, it might actually benefit your credit rating.
Settling debts can have a long-term beneficial effect on your credit score because it allows you to get rid of the debts of the past and move on to building a fresh credit history for yourself. The only negative impact is that future creditors might see that settlements on your credit report and realize that you did not fulfill your end of the bargain of paying back past lenders in full.
An account that has been settled will remain on the credit report for a period of seven years since it was first reported as delinquent. This will have a negative impact on the credit score but the impact will lessen as the information gets older.
You can see the impact on your credit score when you buy your credit score from FICO.com. You are presented with a list of factors that are affecting your credit score negatively. So if you have settled the did in the past and want to see if it is having any sort of a negative impact on your credit score, you should buy your credit score from FICO.com and see the results more clearly.