Fused from two classics: 《荀子·富国》 on 国计 ('national accounting') and 《左传·宣公十二年》's famous line 民生在勤 ('livelihood depends on diligence'). The compound crystallized as a standard policy-level phrase.
register
Political/economic register. Ubiquitous in government statements, news commentary, and policy analyses. Frequent collocations: 关系/事关 + 国计民生; 重大 + 国计民生 + 问题.