We studied the impact of tradelines on credit score change for participants who had a preexisting credit file. 809 participants were included who had a credit score before the addition of authorized user tradelines.

It was found that the average credit score change was 30 points for Experian, 36 points for Equifax, and 40 points for Transunion. The average change in credit score across all three bureaus increased 35 points to the credit score.

This average increase is minor compared to the average score increases for those with no credit file.

93.6%  of the participants in the study started with some credit score. Thus, this is a more appropriate figure to apply to most situations.

Average increases explained.

There are many explanations why these clients saw significantly smaller increases in their scores.

• First and foremost, the lowest FICO score is 350. If clients received any increase in score, they would see at least 350 points. This is an unrealistic expectation for anyone whose credit score is above 500, since the perfect FICO score is 850.
• Additionally, the tradelines added to their reports were no longer the only factor determining the credit score. Instead, they were among many. Since each tradeline contributes to the credit score, having multiple accounts would lessen the impact of new tradelines.
• Finally, it was impossible to guarantee that each account on the participant’s reports was in good standing. Only the authorized user tradelines added were guaranteed to be in good standing. Recent negative factors, like late payments or collections, can negate the benefit of adding a tradeline to a report.
• The clients who had credit files prior to the tradeline were more likely to have negative factors on their reports. This could be why the average improvement in the credit score is limited here.