Paxon - it appears you might be unfamiliar with the LOOKUP function (as opposed to VLOOKUP and HLOOKUP). The formula as written by Pecoflyer using LOOKUP negates the need for complicated, nested IF formulas.

Here is some good info on the LOOKUP formula:
https://support.office.com/en-us/art...1-369d5e3864cb
One statement from that page that applies to your specific instance is:
If the LOOKUP function can't find the lookup_value, the function matches the largest value in lookup_vector that is less than or equal to lookup_value.

Hope this helps!