Hi floss kat and welcome to the forum
When my own clients ask me this question, I generally work out figures based upon the remainder of the contributions payable, plus a fee for actually varying the arrangement, less future fees which will no longer be payable. So your figure would depend upon the amount you are paying monthly, and the length of time remaining in your IVA.
If you go to live abroad, you can continue to make your payments in the usual manner, but do make sure that your IP is aware of your circumstances and has a forwarding address.
Regards, Melanie Giles, Insolvency Practitioner for over 20 years.
For further details contact me at
http://www.melaniegiles.com and view my IVA blog at:
http://melaniegiles.blogs.iva.co.uk