How long should it take me to build up my credit rating?

Okay so I'm 19 and I'll be 20 in a few months, so my credit rating is pretty low and I'd like to build it up for my future so that I can be accepted for things like credit cards, loans and mortgages and things like that. Even mobile phone contracts.

I wanted to apply for a specific credit card a few weeks ago but I didn't get accepted, but it allowed me to earn points on spending and it was who I bank with anyway. So I applied for one of those cards that allows me to build up a credit rating. I've used it a few times throughout the week and I've paid it off straight away through their online system. They also allow me to view my credit score online and it was really poor.

But in all honesty, I'd like to re-apply for the original credit card that I wanted because I can use it abroad and I am going abroad for a few months in the summer time.

So how long should my credit rating take to go up?

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