Paying your credit card or loan bill late will affect your credit score, but it's hard to predict just how many points you'll lose because of a late payment. That's because FICO and other companies who developed credit scoring calculations do not publish the details of their calculation methods. We do have a little insight into how late payments can affect your FICO score at least.
A few years ago, FICO released FICO score loss information based on two hypothetical situations: how a late payment (among other negative actions) would affect a person with a 680 credit score and one with a 780 credit score. In the scenario, the person with 680 credit score (who already had one other late payment on their credit history) would lose between 60 and 80 points for a 30-day late credit card payment, while the person with the 780 credit score (with no other late payments) would lose between 90 and 110 points.
Your credit score might experience a similar drop if you have a credit profile similar to these scenarios. See How Credit Mistakes Hurt Your FICO Score for more information.
You can better predict the impact of a late payment on your credit score using the FICO Score Simulator, available when you purchase the FICO Standard product from myFICO.com. FICO Standard includes your Equifax or TransUnion credit report and credit score.
Just how much your credit score falls after a late payment depends on all the other negative information on your credit report. We do know, however, that a late payment will hurt your credit score by several points. It's better to avoid the late payment and the subsequent damage to your credit score.