We've assumed that around half of those couples would choose to get married (based on a 2010 study by the University of Queensland) and only half of those of these marry within 12 months of marriage equality legislation. Based on an average spend per wedding of $51,000 that could add $500 million to $550 million to the economy in 12 months.
The risks to this figure are to the upside given our conservative assumptions. If half of the population of same sex couples chose to marry within one year, the benefits to the economy in the first year of the legislation would be over $1 billion.
Those figures do not include honeymoon expenditure which would add to the stimulus, especially if foreign couples come to Australia to marry or Australians are encouraged to stay at home, a trend that may be encouraged by the depreciating Australian dollar. Honeymoon expenditures is however difficult to estimate and to some extent, likely to replace existing holiday plans.
As well as the direct economic benefits of weddings, there could be improved social, health and welfare outcomes that would indirectly increase Australia's economic potential.
The security that comes from a marriage would create an effective welfare safety net according to marriage equality lobby group, Australian Marriage Equality as spouses insure each other against a sudden loss of income.
It would also lower levels of stress and mental health problem which are indirect consequences of legal discrimination and social exclusion according to the lobby group.
We could also envisage Australia becoming a more attractive destination for business with several corporations in support of marriage equality preferring to do businesses here and in New Zealand than in other economies in the region. Already a number of employers grant full recognition to the same-sex marriages of their employees and customers.
Whether or not a plebiscite is the means, community pressure for change will remain.
Cherelle Murphy is co-head of Australian Economics and Mandeep Kaura is an economic statistician at ANZ.