How long does it take to raise a credit score?

I just got my credit reports from two of the credit agencies. My score was 550 on one and 625 on the other. I've started to talk to a few collection agencies and have sent payments in full to a few others. My family needs to move sometime this summer. We would like to rent a bigger house... everywhere I... show more I just got my credit reports from two of the credit agencies. My score was 550 on one and 625 on the other. I've started to talk to a few collection agencies and have sent payments in full to a few others.

My family needs to move sometime this summer. We would like to rent a bigger house... everywhere I look online they talk about checking credit ratings. This has me a bit worried.

So, how long do you guys think it will take my credit score to improve after these debts are payed off?

I also, only have one store credit card with a low available credit... I've never been late on that one (I've had it 3 months).

Should I try to get one Visa card, as well, and keep a low balance? Would that help?
Update: That's good to hear about rentals. :-)

I really don't have much on my report. No utilties are on it - good or bad.

The only big thing is what I owe the government in college loans, and, I think I'll be paying that till I die. At least that shows up to date.

Thanks for your answers, guys.
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