Make a list of each item you donate to the thrift store. Create a separate list for each date you make a donation.
Look at a thrift store valuation guide. You may use the valuation guide published by the thrift store you donate to, or use any valuation guide published by national thrift stores, such as the Salvation Army, Goodwill Industries or Arc Thrift Stores. Locate the items from your donation list on the valuation guide.
Consider the condition of your donated item. Valuation guides provide a range of acceptable thrift store values based on the condition of your items. If the item you donated was in fair condition, use a value that is on the lower end of the value range for your item. If the item was in good or like-new condition, select a value that is higher on the value range for your item.
Total the values for each item you donate; based on the date of your donation. You must list the total value of each donation date on IRS Schedule A, Itemized Deduction. If you donate more than $500 worth of goods on any date, you must also complete IRS Form 8283, Noncash Charitable Contributions.