When deducting business expenses on your taxes, it's important to allocate costs accurately between personal and business use. In the case of shared items like plastic poop bags, you should try to estimate the percentage of usage for each purpose. To do this, you can track the number of bags used for your personal dog and for your Wag! clients separately. Once you have determined the usage split, you can calculate the percentage for each and allocate the cost of the plastic poop bags accordingly. For example, if you use a total of 1000 poop bags a year, and 300 are for your personal dog while 700 are for your Wag! clients, then the business use percentage would be 70% (700/1000). If the total cost of the bags was $50, then you could allocate $35 (70% of $50) as a business expense for your dog walking business. Remember to keep accurate records and receipts for all your business expenses, as they will be needed in case of an audit or when filing your taxes.