Whenever a sentence of a court–martial as lawfully adjudged and approved includes a forfeiture of pay or allowances in addition to confinement not suspended, the forfeiture may apply to pay or allowances becoming due on or after the date the sentence is approved by the convening authority. A forfeiture may not extend to any pay or allowances accrued before the date specified in paragraph (1) of this subsection. Subject to paragraph (2) of this subsection, any period of confinement included in a sentence of a court–martial begins to run from the date the sentence is adjudged by the court–martial. Periods during which the sentence to confinement is suspended or deferred shall be excluded in computing the service of the term of confinement. All other sentences of courts–martial are effective on the date ordered executed.