"adaptive" saving?

Hi all,

Have had an idea which I would love to see.

A way of saving a percentage of your wage etc after your essential direct debits have been taken out.

For example -
Allowing me to select which direct debits are essential (Rent/ utility bills).
Then I would assign a percentage of what is left to put into savings (10% etc). Could also be an amount that could leave you with a certain value (Save anything over £500 for example). The savings portion would take place after the specified Direct debits have been saved.

May seem simple but currently I use a standing order but at times a varying direct debit might mean I have to go and transfer money back into my current account from savings.