I usually wash my hands to the elbows when rubbing my arms in Wudu however I sometimes miss out the finger tips is my wudu valid

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

If what is meant is that you do not wash your fingertips in the first wash of ablution, then you wash them in the second or third wash with the intention that it is obligatory to wash them, or you did not intend anything, then your ablution is sufficient.

Ad-Dasouqi stated this in his footnote on Ash-Sharh Al-Kabir as he said: “If a spot [small body part] was not washed the first time, but it was washed the second or third time, then the wash is sufficient.” [End of quote]

In the assumption that you did not wash your fingertips in ablution neither the first time nor after that, then the ablution is invalid. You must repeat the prayers you had performed with this ablution if you know their number. Otherwise, you should continue to repeat the prayers until you think that you are most likely acquitted from sin. This is the view of most scholars.
Nonetheless, Sheikh Al-Islam Ibn Taymiyyah is of the preponderant view that it is not obligatory to repeat previous prayers.

Allah knows best.