How alcohol calories are estimated
Ethanol provides about 7 kcal per gram. This calculator estimates grams as serving volume in millilitres multiplied by alcohol by volume, then by ethanol density, 0.789 g/ml. It multiplies those grams by 7 for ethanol calories. The remaining calories are the difference between that estimate and a typical full-drink energy density from the CheersCount starter catalogue.
Drink recipes and serving sizes vary, so catalogue values are estimates rather than a nutrition label for a particular pour. For mulled wine, this tool uses 87 kcal per 100 ml from Wikifit; your recipe may differ. For custom servings, only ethanol energy is included because no reliable non-ethanol density is available.
Alcohol and food energy
A 2019 systematic review and meta-analysis by Kwok and colleagues found that alcohol calories were not compensated for by eating less food in the studies reviewed. The result describes the evidence across those studies, not what any one person will eat.
Source: Kwok A. et al. (2019), Effect of alcohol consumption on food energy intake: a systematic review and meta-analysis, British Journal of Nutrition, 121(5), 481-495.