I am creating a fundraising database and one of the essential duties it needs
to fulfil is to display when a debt is bad.

In my Events Form I have “Funds Due 1” and “Funds Received 1”

I need the following calculation to appear (in the query, though I don’t
mind where it is done as it will end up in a form) but only if “Funds
Received 1” is empty.

=(DateDiff("d",[Funds Due 1],Now())).

I know I need an IF statement somewhere but I am confused as I am not sure
how this will fit together and also whether it happens in the table, query or
form.

I have tried this:

IIf(IsNull([Funds Received 1])," ",(DateDiff("d",[Funds Due 1],Now())))


but it asks me to Enter A Parameter Value for Funds Received 1 and then
displays the same data as the above calculation :/

The next step is to create a button or message in a form for every Bad
Debt(90 days), which I imagine would be

=IIf([whatever the field is]"90","Bad Debt")