When did you have to wear maternity clothes?

I'm currently 15w3d pregnant with our first baby, and I'm still wearing my regular clothes. Things are shifting, and I have a feeling that I will have to go shopping soon, but so far it seems like my waistline hasn't been affected too much! I am a bigger girl, so I have a feeling that's a big factor. I know everyone is different, but I was just wondering how far along everyone was before you had to switch to maternity clothes. Thanks!