how to hide amounts on incomplete formulae?

I have a list spanning several rows to work out spending amounts.

eg,

L9 is =L8-K9 where K9 is a remaining amount before a purchase and L8 is the purchase making L9 the new remaining amount.

So L10 is =L9-K10, L11 is L10-K11 and so on.

So I've pre-loaded all these formulae in each box so that I don't have to do each one as I go. The problem is that each row has an amount even if the previous cell doesn't. In my case if L3 is say £100, because L4 will be =L3-K4 that will show as £100. Then I see £100 all the way down the list. There is a domino effect.

I hope that makes sense.

What I want to do is keep the formulae, but not have the next cell showing any amount (so be blank) until I put a value into the immediately previous cell.

Is this possible or do I need to ditch the listed formulae?

Use this formula in L4:

=IF(K4="","",L3-K4)

then copy down as required (double-click the fill handle, or drag down).

Hope this helps.

Pete