How can I find out what numbers were used to calculate line 18 Depreciation expense or depletion on Schedule E from last year's taxes?

If you used TurboTax last year, look for the Depreciation and Amortization Report (a TurboTax worksheet, not an IRS form) that is included in your complete return when saved as a PDF. 

 

This report displays each asset, the cost and depreciable basis, as well as the useful life and depreciation convention used to calculate the depreciation expense for the year that is shown on Schedule E Line 18.

 

Most other tax software prepares a similar report.

 

For more help, see How do I get a PDF of my return?