@Laura1980 

Personally, I think a spreadsheet outside of QB is best with a single journal entry, not multiple entries for each fixed asset.  Depending on the volume of depreciation being taken, you can make journal entries to book the depreciation monthly or annually, at year-end.  If you have a material amount of depreciation, I would suggest entering it monthly so it doesn't skew December's numbers and will accurately represent the company's performance on interim financial statements. 

When you make journal entries, you debit depreciation expense and credit accumulated depreciation.  When you track the depreciation of each individual asset on your spreadsheet, you will have a running total of the asset's basis (cost less accumulated depreciation). 

Unless you are required to prepare GAAP-compliant financial statements (if you're posting here, it is unlikely) make sure you are following the IRS schedule for depreciation, not another schedule like double-declining balance or sum-of-years, those do not apply.