Well, you didn't really supply us with enough information to give you the correct answer.
Has your rat just very recently conceived, or is she mid-pregnancy? I'm not sure of exactly the answer you want, but a rat's gestation (time being pregnant) is about 22 days, give or take a few days.
its usually on the 20th to 23th day but mine never gave birth till 25th and it was her first litter.
