An IRS depreciation calculator uses formulas to determine the correct depreciation of property for tax purposes. The Internal Revenue Service advises that investment property and businesses that were acquired or began operating after 1986 should generally use the Modified Accelerated Cost Recovery System.
The General Depreciation System and the Alternative Depreciation System are the two MARCS methods for calculating the correct depreciation for a property. Most properties require use of the GDS method; however, there are cases where the ADS method is required by law. Property must have an effective expected life and be kept for more than one year in order to be eligible for a depreciation deduction, according to the IRS.