On-time payments are the biggest factor affecting your credit score, so missing a payment can really throw you off track. Even if you have otherwise excellent credit, a payment that's more than 30 days past due can knock as many as 100 points off your credit score.
< 30 days late: You probably were charged a late payment fee and perhaps a higher APR, but your credit won't suffer as long as you pay before the 30-day mark. If you’re a first-time offender, call the creditor and ask if they will forgive the fee.
> 30 days late: Bring your account current as soon as possible. Thirty days late is bad, but it’s not as bad as 60, which is not as bad as 90. The sooner you can catch up, the less damage to your credit. When your account is current, you can write a goodwill letter asking the creditor to remove the negative mark – but there’s no guarantee that they will, so make sure to stay on top of your payments.
If it's an error: Credit reports sometimes include mistakes, and errors could increase as many consumers arrange payment accommodations. If you spot incorrect information, it’s important that you dispute the errors ASAP.