Why such a low tax free amount?

Hi all, Last year I was brand new to taxes and self assessment etc and bundled my way through it. Ive just been reviewing my documents and last year I only had a tax free allowance of £3908, and not £12500? Why would this be? I earned just over £110k - is this why? I dont claim benefits of any kind, I was not self employed, I was a standard employee?

Ignore! Yup, understand why