Initial amount. The amount a taxpayer is at risk on the effective date with respect to an activity to which section 465 applies shall be determined in accordance with this section. The initial amount the taxpayer is at risk in the activity shall be the taxpayer's initial basis in the activity as modified by disregarding amounts described in section 465(b) (3) or (4) (relating generally to amounts protected against loss or borrowed from related persons).

Succeeding adjustments. For each taxable year ending before the effective date, the initial amount at risk shall be increased and decreased by the items which increased and decreased the taxpayer's basis in the activity in that year as modified by disregarding the amounts described in section 465(b) (3) or (4).

Application of losses and withdrawals. (1) Losses described in section 465(d) which are incurred in taxable years beginning prior to January 1, 1976 and deducted in such taxable years, will be treated as reducing first that portion of the taxpayer's basis which is attributable to amounts not at risk. On the other hand, withdrawals made in taxable years beginning before January 1, 1976, will be treated as reducing the amount which the taxpayer is at risk.

Therefore, if in a taxable year beginning prior to January 1, 1976 there is a loss described in section 465(d), it shall reduce the amount at risk only to the extent it exceeds the amount of the taxpayer's basis which is not at risk. For the purposes of this paragraph the taxpayer's basis which is not at risk is that portion of the taxpayer's basis in the activity (as of the close of the taxable year and prior to reduction for the loss) which is attributable to amounts described in section 465(b) (3) or (4).

Amount at risk shall not be less than zero. If, after determining the amount described in paragraph (a), (b), and (c) of this section, the amount at risk (but for this paragraph) would be less than zero, the amount at risk on the effective date shall be zero.