Honestly I'd do both month and category - like, separate folders for each month, then within those break it down by business expenses, medical stuff, warranties, whatever applies to you. That way when tax time rolls around you can grab the whole month folder, but if you need to track down a specific warranty claim you're not digging through everything. Some people scan everything with their phone first so they have a backup, which I'm skeptical of at first but it actually saves space and you can search by date or store name on your computer. Just make sure you're keeping receipts for at least three years since the IRS can audit back that far.