BOSTON — Confidence among Massachusetts businesses remained flat during the final month of 2020, as employers ended a tumultuous year with a cautious outlook.

The Associated Industries of Massachusetts Business Confidence Index remained unchanged during December, at 49.3. The reading was 12.9 points lower than in December 2019 but more than 10 points higher than its 2020 low point, in April.

The result reflected solid gains in confidence among employers in the prospects for their own companies and in the Massachusetts economy. Those gains were offset by a 4.8-point drop in opinions about the national outlook.

The AIM Index, based on a survey of more than 140 Massachusetts employers, is calculated on a 100-point scale, with 50 as neutral; a reading above 50 is positive, while below 50 is negative.