In corporate finance, in the context of discounted cash flow valuation, the forecast period is the time period during which explicitly forecast, individual yearly cash flows are input to the valuation-formula.
Cash flows after the forecast period are represented by a fixed number - the "terminal value" - determined using assumptions relating to the sustainable compound annual growth rate or exit multiple.
There are no fixed rules for determining the duration of the forecast period.
However, choosing a forecast period of 10 years, for example, will not be meaningful when individual cash flows can only reasonably be modeled for four years; see Cashflow forecast.
Addressing this, there are three typical methods of determining the forecast period.