Hello Neil,

I assume your formula should be like this:

=MAX(IF($C3:$C66>=$S$5,$G$3:$G$66))

[you don't need the zero]

This is an "array formula" which means that you won't get the correct result unless entered with CTRL+SHIFT+ENTER

To do that....

Put formula in a cell and select that cell. Then press F2 key and hold down CTRL and SHIFT keys while presing ENTER. Curly braces like { and } will appear around the formula in the formula bar