This is the first article to explore partner correlations across Body Mass Index (BMI) categories for couples in long‐term, stable relationships using data from the Household, Income and Labour Dynamics in Australia Survey 2006–2011. The moderating effects of three hypotheses on this correlation are tested: (i) selection; (ii) relationship stability; and (iii) social obligation or environment. The results show gender‐asymmetric effects in the correlation in BMI categories. Selection explains the majority of the correlation for men and all of the correlation in BMI categories for women. Some evidence of variables related to stability and social obligation are significantly associated with weight outcomes for men.