Can a trustee and beneficiary of a irrevocable trust gift money to the same trust, if so how much is allowed and does the trust have to pay taxes on such a gift ?

[M-MTax]

The grantor can add money to the trust unless there is some specific prohibition which is not very likely.

It's not a gift if you give something to yourself. This would be nothing more than a deposit......a transfer of money to the trust which the trustee-bene already owns.

[zjlc67]

Sounds like this person is dealing with a now irrevocable trust (started as grantor revocable trust) — would now be irrevocable if parent passed.  Sounds like they are the trustee as well as a current beneficiary.  

To make it their own grantor trust (revocable), they would have to transfer all of the current irrevocable trust’s assets into the new grantor trust.  An expensive move. 

If the current irrevocable trust cannot afford the upkeep of its asset(s), the trustee can pay out of pocket and get paid back by the trust at a later date once funds are available (presumable from selling an asset). 

This is to the best of my understanding.

[M-MTax]

They don't have to transfer anything, actually. 

Irrevocable trusts can still be grantor trusts under certain circumstances.