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The general formula for determining the pre-money value (PRE) is to first discount the exit (sale) value at the appropriate discount rate to its present value. This value is called the post-money value (POST). The pre-money value is the post-money value less the investment (INV):

POST = FV / (1+r)^N
PRE = POST − INV

This would yield a PRE value of $7.24 million when using the unadjusted discount rate of 25%. This rate, however, must be adjusted for the possibility of failure in any particular year. This is calculated as follows:

r* = (1 + r) / (1 − q) − 1, where r is the unadjusted discount rate and q is the probability of failure.

The discount rate adjusted for failure is then:

r* = (1 + 0.25) / (1 − 0.20) − 1 = 0.5625 or 56.25%

The pre value is then calculated as:

POST* = $25 / (1.5625)4 = $4.19 million.
PRE* = $4.19 − $3.0 = $1.19 million.