On Sep 1, 2:42 pm, "Ed" wrote:
I found the following formula, using interpolation. It will start by
assigning a 50% markup to $1.00 and the percentage will go down from there
until it reaches $39.99; and will start at 12% for anything above $40.00.

=IF(A1<=39.99,(-A1/100+0.50+1/100),0.12)

I would like to know how I can add to the formula so that it starts and ends
at 14 different intervals:

Did you mean 24 percent groups since you listed 24? The ones you
listed are not linear or predictable in any mathematical way, so one
formula won't cut it, you'll need several to get all those different
percents. BTW, that formula will not give you exactly the right
amount, you'd need to add a rounding. IE: $7.50 cost equals a percent
of 43.5, not 44 even. So:
=IF(A1<=39.99,ROUND(-A1/100+0.50+1/100,2),0.12)

However, unless you want a long series of IF statements for a formula,
why not use a lookup table? Put the table on a separate worksheet, out
of the way of your invoice. Or use the "table within a formula" as
shown in Gord's link, but in a LOOKUP function:
=LOOKUP(A1,{1;2;3;4,etc},{0.5;0.49;0.48;0.47,etc})

For an actual table:
You can just enter the table like you have typed here (you would need
to take out the ranges, just use $1,2,3...), and use the Index/Match
formula I gave for a lookup. Although I designed it with the highest
cost number at the top. So:

40.......12%
35.......14%
30.......16%
etc