I've seen some interesting applications of rates applied with various intentions and there are some quirks and rules that make depreciation a task for experts. If you're doing your own tax return with self-employed income it doesn't hurt to get your depreciation calculations reviewed — you may get a better rate out of an expert or you may save yourself penalties.
Recovering from depreciation
The sale of an asset for more than it is worth in the books can trigger what they call depreciation recovery. Say you buy a tool for $1000, it depreciates to $500. If you sell it for $900 the difference between the $500 depreciated value and its sale value of $900 is income. This $400 difference is depreciation recovery and, yes, you pay tax on that income.
Jeremy Tauri is an associate at Plus Chartered Accountants.