Introducing New Rats?

It's good to hear you are both increasing the cage size, and getting her a companion. She will be very happy!

Introductions do not happen right away. If you have not yet read up on proper introduction methods, as well as quarantine, please do so. Quarantine takes at least two weeks, and introductions no less than one week. In this time, the rats need to live in two separate cages, while meeting daily on neutral surfaces.

Afterwards it's a good idea to move them intro a brand new cage, so there is no residual scent. But you can also just scrub the cage as clean as possible. So to answer your question, it really does not matter, but I would go ahead and move her into a larger cage right away. There is no excuse for keeping any pet in a cage that's too small for it, she will appreciate more space.

Also a tip on the new rat, try to find an older female. Girls tend to bully babies, whereas another adult will stand up for herself, and less fighting will occur.

You should purchase the new cage now and introduce them in December. You don't want to just put the two rats in a cage together. Introduction is a process, and if it's not done right there can be trouble. I say purchase the new cage now because you'll need two cages for the introduction process. You'll be housing them seperately for about a week or so, so the new rat can first get used to you. During that week you can set the two cages on the floor beside eachother with the rats in them so they can smell each others scents. Just make sure the cages aren't too close. If you want, after you do that you can take the rats out and switch the cages. Let one run around in ones cage, and one run around in the other rats cage that way they can smell everything and get the feel of the new rat. After that week, you want to introduce them. Make sure you introduce them in a neutral territory, a place the first rat hasn't played before. That way the first rat won't be territorial. There will be some butt sniffing, and the first rat may try to climb over top the new rat. That's just to show dominance. Or the new rat may even try to climb under the other rat to show that they're not a threat. Let them meet a few times then put them in the cage together with you supervising and see how it goes.

Agree with most of what has been said.

Except - Oxygen's comment about girl rats bullying babies. It is not unknown, but most girl rats bully boy rats. A young female is likely to be well and quickly accepted (although there can be a clash of personalities - I have found this rare in the girls).

And yes - get both cage and rat ASAP!!!

You have one lonely and deprived rat in your house - she just can't speak for herself.

(But I am totally glad you have her best interests at heart and will be getting her some company very soon - means a lot.)

First of all, Rats shouldn't live alone. I would suggest getting the new rat as soon as possible. The cage should be purchased soon too.

Well rats are social so I would just put them in your new cage and just watch to see if they get along. They probably will. But if you don't like that idea you can get the new cage and put one in it and one in the old cage and put the cages back to back to see what they do then introduce them in an enclosed room

Good luck :P