Multiplying a currency field - Calculated fields

Hi all,

I have a field where I want it to give me either 80% or 20% of another calculated fields value. 

I went for the easy route of:

multiply($ut_contract_value_c,0.2)

But I get an error message saying the field needs to be a number and it's currency. 

I tried subtract, but that just takes off 20 pence instead of 20%.

Any ideas how I can do this easily without having to edit the original calculated field to use for this one?