Delinquencies are "huge influences" on the credit score, says Stephen Brobeck, executive director of the Consumer Federation of America. In fact, they make up 35 percent of your FICO score.
If you see notations that bills have been paid 30, 60, 90 or 120 days late, "that's very damaging" to your credit, he says.
The other factor that's important here: the timeline. How late was the payment, and how long ago did you make this mistake?
The later the payment, the more it hurts your credit, says Evan Hendricks, author of "Credit Scores & Credit Reports: How the System Really Works, What You Can Do."
But the more time that has passed since you made a late payment, the less it will affect your credit, he says.