This is a list of the best-selling albums by year in the United States, published by American music magazine Billboard since 1956 as year-end rankings of album sales. Until 1991, the Billboard album chart was based on a survey of representative retail outlets that determined a ranking, not a tally of actual sales. Weekly surveys and year-end charts by Billboard and other publications such as now defunct Cash Box magazine sometimes differed. For instance, during the 1960s and 1970s, the number-one album as determined by these two publications differed in 10 out of 20 years. From 1992 onwards, the Billboard year-end and weekly charts were calculated by Nielsen SoundScan. Note that this slightly differs from prior Billboard year-end album charts, which were a measure of chart performances over twelve months from around December to November rather than actual total sales. In addition, certain additions post-2015 may differ from best-selling albums in the United States of the Nielsen SoundScan era, which includes album-equivalent units by means of streaming.