Return number of days until a date found in a lookup table

I have been, for days (!), trying to get a formula that will allow me to calculate the number of days from a date in a cell to an end date that can be found in a lookup table. Basically, the form I'm developing requires you to enter a capitalisation date and I want to calculate the number of days between that date and the end of that fiscal year. So I've written a table with the years in it and the corresponding end date of that fiscal year. The cap date will be an input and I want the rest to calculate from there. I've gotten the "datedif" function to work if I link directly to that end date in the table, but that end date will change depending on what they input- so struggling to build from that! Any suggestions?! Thanks!