Straight-Line Depreciation:
Annual Depreciation = (Cost - Salvage Value) / Useful Life
Declining Balance Depreciation:
Depreciation Rate = (2 / Useful Life) × 100
Annual Depreciation = Remaining Value × Depreciation Rate
Sum of Years Depreciation:
Total Years = (n × (n + 1)) / 2
Annual Depreciation = (Cost - Salvage Value) × (Remaining Years / Total Years)