It's safe but its impact is probably dependant on what your utilization level is now and what it will be. Movingforward's was low and just got lower. lol. I am doing something similar...we are paying about 30 % of my wife's utilization down, and then she's been added to a $7600 card with a zero balance. No credit inquiry, no late payments...and her utilization should be be around 32% from about 84% in a month or two. We don't need a ton of points, so hopefully this will do the trick. I can update what the impact on her score is once it happens but you may not want to wait another 5 or 6 weeks.
Yeah my utlization is a little higher becaise we transferred most of our debt on to one card. I have done the math and I *think* if I can add another $8k of available credit it may put me below 40%. I just don't want to do it if there is some unknown "gotcha" that will make my score drop or something. On pins and needles constantly over that stuff
Just as an update, I added my wife to a credit card as an authorized user and the card reported to Equifax just in the past couple of days. In addition, we paid off about 40% of her utilization (her utilization percentage prior to being added to the new card) and her score jumped to 652 from 629. The card added $7600 in available credit with a zero balance. Since we only need her mid-score to reach 640, we believe we've pretty much gotten there, though the plan is to pay down even more debt.
Her Transunion score continues to go down on this site for whatever reason, but the TU98 score available here isn't really used by anyone to begin with. Also, the report isn't updated with the information that hit the Equifax report - in fact, the balance on the card we paid down wasn't showing the lower amount yet. So they probably haven't reported to TU yet.
Anyway, it would be nice to know where the other scores are at - Experian, and the transunion model our lender uses, but based on the last lender pull in December, her Equifax score was the lowest of the three- 614, and that matched what we saw here. Probably not safe to assume anything ever, but her Experian and Transunion scores were both higher than Equifax so we, again, we believe the credit scores are where they need to be now.