# 6. Depreciation

6. Depreciation
Depreciation, or loss of value over time, represents the consumption of an asset’s benefits over its useful life. Three approaches are presented here for calculating depreciation. The most straightforward approach is to represent depreciation as a function of asset age using a simple linear relationship. Where condition data are available, it may be preferable to supplement or replace asset age with a calculation of effective age based on condition. A third approach is to analyze the pattern benefit consumption to establish a non-linear calculation of depreciation.

General Guidance

Depreciation is the “loss of value of an asset or class of assets, as they age” (1), which may be approximated by the asset’s deterioration or decline in physical condition. This section introduces three approaches to depreciation: asset’s actual age, asset condition, and non-linear benefit consumption. After describing their strengths and weaknesses, the section offers a flowchart which assists in choosing an appropriate approach.

Recommended Steps

This section describes the specific steps involved using the three different depreciation approaches addressed in this chapter: linear depreciation based on actual age (“age-based”); a linear-based depreciation using a condition-based approach (“condition-based”); and non-linear depreciation established through analysis of the pattern of benefit consumption (“non-linear”).

Note that the steps presented here describe the case in which depreciation is calculated for an individual asset or component since the point at which the initial value was calculated as described in Chapter 4, or since the last treatment, if a treatment was performed more recently than the time of the initial value calculation. However, depreciation can be calculated for other contexts using the same basic steps. For instance, one can use the steps described here to calculate the cumulative depreciation of an asset looking back in time prior to a recent valuation, predict future depreciation when testing different scenarios or treatment assumptions, or calculate depreciation for an inventory rather than an individual asset.

Examples

The following are hypothetical examples illustrating the different depreciation approaches described in Section 6.2.

Practice Assessment

This section provides examples of “emerging,” “strengthening,” and “advanced” practices with respect to calculation of depreciation. Maturity levels are defined for each of the for two basic cases described in the guidance, that one has age data, or that one has condition data. In both cases there is an additional option to assume a linear pattern of depreciation with respect to age/effective age, or to perform a supplemental analysis to analyze the pattern of benefit consumption for the asset. In the table an emerging practice is one that supports the guidance with minimal complexity, an advanced practice illustrates a “state of the art” example in which an agency has addressed some aspect of the asset value calculation in a comprehensive manner, and strengthening practice lies between these two levels.