from IRS reg, 1.183-1
(d) Activity defined -
(1) Ascertainment of activity. In order to determine whether, and to what extent, section 183 and the regulations thereunder apply, the activity or activities of the taxpayer must be ascertained. For instance, where the taxpayer is engaged in several undertakings, each of these may be a separate activity, or several undertakings may constitute one activity. In ascertaining the activity or activities of the taxpayer, all the facts and circumstances of the case must be taken into account. Generally, the most significant facts and circumstances in making this determination are the degree of organizational and economic interrelationship of various undertakings, the business purpose which is (or might be) served by carrying on the various undertakings separately or together in a trade or business or in an investment setting, and the similarity of various undertakings. Generally, the Commissioner will accept the characterization by the taxpayer of several undertakings either as a single activity or as separate activities. The taxpayer's characterization will not be accepted, however, when it appears that his characterization is artificial and cannot be reasonably supported under the facts and circumstances of the case. If the taxpayer engages in two or more separate activities, deductions and income from each separate activity are not aggregated either in determining whether a particular activity is engaged in for profit or in applying section 183. Where land is purchased or held primarily with the intent to profit from increase in its value, and the taxpayer also engages in farming on such land, the farming and the holding of the land will ordinarily be considered a single activity only if the farming activity reduces the net cost of carrying the land for its appreciation in value. Thus, the farming and holding of the land will be considered a single activity only if the income derived from farming exceeds the deductions attributable to the farming activity which are not directly attributable to the holding of the land (that is, deductions other than those directly attributable to the holding of the land such as interest on a mortgage secured by the land, annual property taxes attributable to the land and improvements, and depreciation of improvements to the land).
also the reg subsection (b)(4)
(4) Rule for capital gains and losses -
(i) In general. For purposes of section 183 and the regulations thereunder, the gross income from any activity not engaged in for profit includes the total of all capital gains attributable to such activity determined without regard to the section 1202 deduction. Amounts attributable to an activity not engaged in for profit which would be allowable as a deduction under section 1202, without regard to section 183, shall be allowable as a deduction under section 183(b)(1) in accordance with the rules stated in this subparagraph.
(ii) Cases where deduction not allowed under section 183. No deduction is allowable under section 183(b)(1) with respect to capital gains attributable to an activity not engaged in for profit if:
(a) Without regard to section 183 and the regulations thereunder, there is no excess of net long-term capital gain over net short-term capital loss for the year, or
(b) There is no excess of net long-term capital gain attributable to the activity over net short-term capital loss attributable to the activity.
(iii) Allocation of deduction. If there is:
(a) An excess of net long-term capital gain over net short-term capital loss attributable to an activity not engaged in for profit, and
(b) Such an excess attributable to all activities, determined without regard to section 183 and the regulations thereunder, the deduction allowable under section 183(b)(1) attributable to capital gains with respect to each activity not engaged in for profit (with respect to which there is an excess of net long-term capital gain over net short-term capital loss for the year) shall be an amount equal to the deduction allowable under section 1202 for the taxable year (determined without regard to section 183) multiplied by a fraction the numerator of which is the excess of the net long-term capital gain attributable to the activity over the net short-term capital loss attributable to the activity and the denominator of which is an amount equal to the total excess of net long-term capital gain over net short-term capital loss for all activities with respect to which there is such excess. The amount of the total section 1202 deduction allowable for the year shall be reduced by the amount determined to be allocable to activities not engaged in for profit and accordingly allowed as a deduction under section 183(b)(1).
(iv) Example. The provisions of this subparagraph may be illustrated by the following example:
Example.
A, an individual who uses the cash receipts and disbursement method of accounting and the calendar year as the taxable year, has three activities not engaged in for profit. For his taxable year ending on December 31, 1973, A has a $200 net long-term capital gain from activity No. 1, a $100 net short-term capital loss from activity No. 2, and a $300 net long-term capital gain from activity No. 3. In addition, A has a $500 net long-term capital gain from another activity which he engages in for profit. A computes his deductions for capital gains for calendar year 1973 as follows:
Section 1202 deduction without regard to section 183 is determined as follows:
Net long-term capital gain from activity No. 1 $200
Net long-term capital gain from activity No. 3 300
Net long-term capital gain from activity engaged in for profit 500
Total net long-term capital gain from all activities 1,000
Less: Net short-term capital loss attributable to activity No. 2 100
Aggregate net long-term capital gain over net short-term capital loss from all activities 900
Section 1202 deduction determined without regard to section 183 (one-half of $900) $450
the example would seem to suggest that for not for profit activities capital gain from one activity can be offset by capital loss from another - but not below zero
the 1202 deduction as of today relates to partial exclusion of gain on small business stock. it would not make sense to limit this exclusion because of a not-for-profit capital loss unless this loss could actually be used in computing net capital gains for income tax purposes. this is my opinion and others may disagree.
