How to fix my iferror when having to removed data

[EstherMiles]

My calculation is =IFERROR(C15-B15+1,0) but when I remove that data from a field it leaves 1.

I need to calculate the number of checks I am working with so check number 1234 is my beginning check number and my ending check number is 1239, that is a total of 6 checks.  that is why i'm adding the +1 in my formula, but when I remove the data it leaves a 1 in my total column. 

When the fields are blank my total is 0, but in a field that had data and then I remove it I am left with 1 when the data is removed and now blank.

[#2]

@EstherMiles Well, blank cells represent a value of zero, so 0-0+1 = 1. Having blank cells doesn't generate an error, so IFERROR does nothing here

Try something like this in stead:

=(C15-B15+1)*NOT(OR(ISBLANK(B15),ISBLANK(C15)))

It will do the calculation provided that both B15 and C16 contain data.

[#3]

@EstherMiles 

As variant

=IF( C15*D15, D15-C15+1,)