You should determine the percentage of business use for each expense based on factors, such as usage time or the number of users. Maintaining detailed records of business and private will help to support your claim. Then, apply the business-use percentage to the total expense to calculate the deductible amount. For example, if you use a software subscription for 80% business use and 20% personal use, you can claim 80% of the expense as a tax deduction. Ensure you record how you arrived at the business-use percentage to substantiate your claim.