Which accounting principle allows an investor to write off their investment in income-producing property over time?

The correct answer is tax depreciation because this accounting principle allows property owners to deduct the cost of their investment in income-producing properties over a specified period. Tax depreciation recognizes that assets, such as buildings, wear out or lose value over time due to factors like usage and age. By allowing the investor to write off a portion of the value of their investment annually, tax depreciation can reduce taxable income, thereby providing significant financial benefits.

In contrast, the other options do not pertain to the write-off process relevant to income-producing properties. Market value adjustment refers to changes in the property's market value but does not directly impact the accounting treatment of the property's cost. Asset appreciation deals with the increase in value over time, while cost allocation refers to how costs are distributed among various projects or departments rather than the depreciation of assets for tax purposes. Thus, tax depreciation is the principle that directly supports the ability to write off the value of an investment in income-producing properties over time.