The gender pay gap has narrowed substantially since the Equal Pay Act was signed in 1963. Still, the typical woman working full time in the United States earns $40,022 a year — or only about 80% of the median annual income for men working full time of $50,119.

A study conducted by the Pew Research Center estimates a woman would need to work an additional 44 days a year to earn the same amount as her male counterpart.

Several explanations — some real, some imagined — are often given to account for the discrepancy. For example, women typically are out of work longer during pregnancy, women leave the workforce sooner, and women are more likely to pursue lower-paying careers. However, even when accounting for all these factors, there still appears to be a gap.

In the Boston metro area, the wage gap closely matches that of the nation. The typical woman working full-time in Boston earns $52,381 a year, or about 79.1% of the $66,211 median income of men in the metro area.

Differences in pay between men and women varies widely throughout Massachusetts. Of the five metro areas in Massachusetts, three have a smaller gender wage gap than Boston.

The gender pay gap in Boston also varies by industry. The largest earnings gap between men and women in the metro area can be found in farming, fishing, and forestry occupations, where women earn only 58 cents for every dollar earned by men.

In Boston’s construction and extraction occupations, the typical female earns 148.5% of what the typical male earns. However, women comprise only 2.3% of total employment within the industry, which itself is relatively small, so the higher wages do little to meaningfully improve the overall wage gap.

The pay gap also tends to be worse in professions in which women have historically been excluded. The typical female in the sales profession in Boston, for example, earns only 74 cents for every dollar a man in the field earns.