It will improve your AAoA (so long as they both report AUs, and I think they do but have not checked), but as to how much it will improve, that depends on how many other tradelines you have on your report. Assuming you have only credit cards, and assuming you have only two credit cards that are 3 months old, if you add both of your parents cards, your AAoA goes to just over 5 years. If you have three cards, it is just over 4 years. Four cards, three and a half years. And so on.
You just have to sum the age of all of the accounts on your report and then divide by the number of accounts. You didn't mention car loans, student loans, etc., but include those if you have any.
Starting Score: ~500 (12/01/2008)
@rootpooty wrote:
I have 3 cards with no loans or car payments or anything. So if I got added my AAOA would be 4 years? What would that do to my score?
If they added you as AU on just one of their cards it should bring your AAoA's to 2.5 years (FICO rounds down AAoA's) so your AAoA's would be 2 years.
If they added you on both cards your AAoA's would be 4.9 yrs, actually 4 yrs because of the rounding down. (hoping my math is correct 
)
Not only would it help your AAoA's it will help you with util, because you will also inherit their CL or CL's if you were added on both.
But to tell you what kind of increase you would see is just a guess and only a guess, and my guess would be anywhere from 0-25 points YMMV
When I was added as AU on my Fathers AmEx opened in 84, I had pretty close to the same profile you have, but I had 4 cards, and they were just a tad older than yours, and I gained 27 points TU and like 22 points EQ.
One thing that I believe, being an AU is not going to make it any easier to get a better CC or higher limits, because I firmly believe that when apping for a CC the CCC you are apping with will not take the AU accounts into consideration when making their decision, I may be way wrong here, but, based on my experiences in the past, having my Fathers 27 yr old card (16K CL) did not net me huge CL's or instant approvals, yes it raised my scores but the creditors want to really see your history, not your parents history.
Just my .02 cents.
EDITED: to correct my math I was wrong (I think LOL) I think I have it right this time
@Anonymous wrote:
@rootpooty wrote:
I have 3 cards with no loans or car payments or anything. So if I got added my AAOA would be 4 years? What would that do to my score?If they added you as AU on just one of their cards it should bring your AAoA's to 2.5 years (FICO rounds down AAoA's) so your AAoA's would be 2 years.
If they added you on both cards your AAoA's would be 4.9 yrs, actually 4 yrs because of the rounding down. (hoping my math is correct
Not only would it help your AAoA's it will help you with util, because you will also inherit their CL or CL's if you were added on both.
But to tell you what kind of increase you would see is just a guess and only a guess, and my guess would be anywhere from 0-25 points YMMV
When I was added as AU on my Fathers AmEx opened in 84, I had pretty close to the same profile you have, but I had 4 cards, and they were just a tad older than yours, and I gained 27 points TU and like 22 points EQ.
One thing that I believe, being an AU is not going to make it any easier to get a better CC or higher limits, because I firmly believe that when apping for a CC the CCC you are apping with will not take the AU accounts into consideration when making their decision, I may be way wrong here, but, based on my experiences in the past, having my Fathers 27 yr old card (16K CL) did not net me huge CL's or instant approvals, yes it raised my scores but the creditors want to really see your history, not your parents history.
Just my .02 cents.
EDITED: to correct my math I was wrong (I think LOL) I think I have it right this time
On the math, not sure what you were using, but assuming parents cards are exactly 10 years old, its 240 months for parents cards, then 9 months for his cards, 249 months divided by 5 is 49.8, divide that by 12 for years, and it is 4.15 years. That's why I said just over 4 years. You got 4.9 years, so maybe we are using different assumptions about the age of his parents cards.
@Walt_K wrote:
@Anonymous wrote:
@rootpooty wrote:
I have 3 cards with no loans or car payments or anything. So if I got added my AAOA would be 4 years? What would that do to my score?If they added you as AU on just one of their cards it should bring your AAoA's to 2.5 years (FICO rounds down AAoA's) so your AAoA's would be 2 years.
If they added you on both cards your AAoA's would be 4.9 yrs, actually 4 yrs because of the rounding down. (hoping my math is correct
Not only would it help your AAoA's it will help you with util, because you will also inherit their CL or CL's if you were added on both.
But to tell you what kind of increase you would see is just a guess and only a guess, and my guess would be anywhere from 0-25 points YMMV
When I was added as AU on my Fathers AmEx opened in 84, I had pretty close to the same profile you have, but I had 4 cards, and they were just a tad older than yours, and I gained 27 points TU and like 22 points EQ.
One thing that I believe, being an AU is not going to make it any easier to get a better CC or higher limits, because I firmly believe that when apping for a CC the CCC you are apping with will not take the AU accounts into consideration when making their decision, I may be way wrong here, but, based on my experiences in the past, having my Fathers 27 yr old card (16K CL) did not net me huge CL's or instant approvals, yes it raised my scores but the creditors want to really see your history, not your parents history.
Just my .02 cents.
EDITED: to correct my math I was wrong (I think LOL) I think I have it right this time
On the math, not sure what you were using, but assuming parents cards are exactly 10 years old, its 240 months for parents cards, then 9 months for his cards, 249 months divided by 5 is 49.8, divide that by 12 for years, and it is 4.15 years. That's why I said just over 4 years. You got 4.9 years, so maybe we are using different assumptions about the age of his parents cards.
I had the same exact calculations as you did up to the point I highlighted red, I knew I was forgetting something, as you can see I had the 49.8 and that's where I came up with 4.9 yrs, I forgot about the divide that by 12 part.
Thank you Walt_K for refreshing my memory on how to calculate AAoA's.
@rootpooty wrote:
So would I benefit at all by being an AU on the cards?
Maybe. You're likely to see at least some score increase from the added age. The increased credit limit will help with your utilization, but if your parents run their cards at high utilization, that will negatively affect you. Even if they pay their bills in full every month, if they wait until after their statement cuts to pay their bills, that could have you showing high utilization.
For example, let's say your parents have a CL of $5K on one of the cards but they charge about $3-$4K per month. If they wait until after they get their bill to pay, like most people, that card is going to report at 60-75% utilization every month. Your overall utilization will depend on total balance reported divided by total credit limits.
If I had to guess, unless your parents are running very high balances constantly, on the whole, this will help you. As long as you're not in a time crunch, there's no downside to adding them. If it hurts your score, you can always cancel the AU cards and have them removed from your report. It may take a few months to have them removed, and sometimes you have to file a dispute, so be careful if you are doing this with the intent to apply for some big purchase in the near term. But if you just want to see how it will affect your score and you have time to have them removed if you don't like it, go ahead.