I have many clothing items that I plan on donating to a local charitable/religious organization. I want to include the value of these items as a charitable deduction on my income tax, but I don't know how to calculate the value of these items. Do I use a percentage of the original Suggested Retail Price? Or a percentage of the price I paid for them?
The value of your used clothes is the fair market value of the items. If you are donating to the salvation army or GoodWill you can walk through the store to an idea of what they are going to sell your items for or you could use something like this guide provided by the salvation army. For more information on donating items you can look at this publication from the IRS.
Keep in mind, the IRS shows on choice for "how valued" as "consignment shop value." The Goodwill guide is just that, a guide, low for some items (a man's $600 suit a few years old, hardly worn, is not worth just $72) and high for others (a black and white TV has no value. I could not find a charity that would even take a tube television. I left it on the sidewalk with a note that said "works" and it was gone, picked up by a passing car.)
In general, consignment shops will charge about 1/3 retail. For household items, check eBay listings to justify valuation.
I usually file my taxes with H&R Block's TaxCut software (now called H&R Block At Home).
H&R block provides a tool called DeductionPro that lets you enter quantities of various items donated (Men's T-Shirt, pair of Women's Shoes, etc), and it has pre-assigned values. So, it does all the math for you.
DeductionPro has a "printable" worksheet option, where it prints a list of all items and you can fill in the blanks. Before dropping off a donation, I usually print one of these worksheets, and mark down all of the items I will be donating. Afterward, I staple the worksheet to the receipt from Goodwill. When I do my taxes in April, I enter all of printed worksheets into DeductionPro.
The latest version of DeductionPro is web based, so I think you can use it to print worksheets even if you aren't an H&R Block customer. https://www.deductionpro.com/
I prefer to use a third-party tool vs coming up with my own valuation, because if the IRS ever questions me, I can blame H&R Block.
If you are a TurboTax user, they have a similar tool.