Me:
- Credit Score (790+) from CreditKarma.com
- 5 Open Accounts (Chase, AMEX, AMER HONDA, Target, Macys)
- Age of Credit History: 4 Yrs, 6 Mos
- I got my SSN in July/August 2006
Wife:
- Credit Score (780+) from CreditKarma.com
- 2 Open Accounts (Chase, AMEX - They both all authorized holders of my Chase/AMEX accounts)
- Age of Credit History: 4 Yrs, 1 Mo
- She just got in August, 2015
How quickly she has gained the credit (but is CreditKarma.com accurate is enough?), though I added her as Authorized Card Holder only 2 years ago for Chase, and 1 year ago for AMEX.


My questions:
1. Should she apply for new credit accounts (because she has no credit account, besides two Authorized Card Holders of my Chase/AMEX)?


2. If so, should she also add me as Authorized Card Holder?


3. Should I apply for more credit accounts (CreditKarma.com tells me that I have too few accounts)?


4. If so, should I also add her as Authorized Card Holder?


5. If I apply for new credit accounts or my wife added me as Authorized Card Holder, my Age of Credit History will be lowered down (though Total Accounts are increased). Is it good? Because the impact for Age of Credit History (Medium Impact), while Total Accounts (Low Impact)


6. Or should just apply for Joint Accounts?


7. When applying for 2 or more new credit accounts, should I apply for all of them at once or separately (3+ months later for the next account)?


8. Anyway, if we both have 780+ credit score, we will get very nice low interest loan rate for buying a house, right?
Or do we still need to build higher credit scores?

The amount of credit to income is looked at, if you have too many credit cards it can be negative.

The number of credit inquiry (apply for credit cards) can also be negative. As with the age of cards.

What is not seen id debt to income ratio, also important, and also any late pays.

The one question is why do you want more credit? Merely to attempt to purchase home ?
Do you currently have loan on house?

@Fr_Chuck, thanks for your reply.We don't have a house loan yet (I do have the AMER Honda auto-loan), the main purpose to have more credit accounts is to build up more credit to get lower interest rate for purchasing a home.

Furthermore, my wife does NOT even have a single credit account (as a primary holder).

Our total debt (mainly from the Honda auto-loan) is only around ~ 8K, and our yearly gross income is around 250k ~ 300k.

Wife doesn't NEED a card in her name... her being on your card gives her a credit history as well. And of course if she was less than responsible with it... it would negatively impact you as well.

And having been trough the Mortgage thing a bunch of times as rates kept dropping lower and lower over the last 15 years and what has been explaned to me by the banks and financial advisers.

You have a 790. That's pretty good, actually its VERY good, 850 is a perfect score and very, very difficult to achieve. You will get the better rates with a number that high. Opening a few credit cards may cause your score to dip. Because that gives you more available credit... and going into a new or refinanced mortgage... it raises red flags as to WHY you are trying to get this extra credit all of a sudden. You really don't want or need more than one or two major credit cards. With your income level they will likely have a very high limit.