Average rate of employees' social security contributions for a single person with two children in OECD countries

Single persons: Unmarried men and women.
Couple with two children: Married couple with two dependent children between six to eleven years of age inclusive.
Labour costs: The sum of gross wage earnings, employers’ social security contributions and payroll taxes
Net income after taxes: Gross wage earnings less the sum of personal income tax and employee social security contributions plus cash transfers received from general government
Personal average tax rate (tax burden): The sum of personal income tax and employee social security contributions expressed as a percentage of gross wage earnings.
Tax wedge: The sum of personal income tax, employee and employer social security contributions plus any payroll tax, less cash transfers expressed as a percentage of labour costs.

The Report focuses on eight different family types which vary by household composition and level of earnings.
Each household contains a full-time adult employee working in one of a broad range of industry sectors of each OECD economy. Some of the households also have a spouse working less than full-time.
The annual income from employment is assumed to be equal to a given fraction of the average gross wage earnings of these workers.
Additional assumptions are also made regarding other relevant personal circumstances of these wage earners in order to calculate their tax/benefit position.
Indicators expressed in US dollars are converted using PPP exchange rates

http://www.oecd.org/ctp/tax-policy/taxing-wages-20725124.htm
For New Zealand specific calculations: http://www.keepeek.com/Digital-Asset-Management/oecd/taxation/taxing-wages-2017/new-zealand-2016-17-income-tax-year_tax_wages-2017-32-en#.Wbi1LMgjHyQ#page8

The simple approach of comparing the tax/benefit position for eight model families avoids many of the conceptual and definitional problems involved in more complex international comparisons of tax burdens and transfer programmes. However, a drawback of this methodology is that the earnings of an average worker will usually occupy a different position in the overall income distribution in different economies, although the earnings relate to workers in similar jobs in various OECD Member countries.
Because of the limitations on the taxes and benefits covered in the Report, the data cannot be taken as an indication of the overall impact of the government sector on the welfare of taxpayers and their families.

Public Sector, Taxation and Market Regulation > Taxation > Taxing Wages > Country tables (current model) > Export > Text file (CSV)

This annual publication provides details of taxes paid in wages in all thirty-four member countries of the OECD, providing unique information for each of the OECD countries on the income taxes paid by workers, their social security contributions, the family benefits they receive in the form of cash transfers as well as the social security contributions and payroll taxes paid by their employers.
The amounts of taxes and social security contributions paid and cash benefits received are set out, programme by programme, for 8 different household types characterised by marital status, number of children, earnings levels expressed as proportion of average wages and whether there are one or two earners.
The results reported include the average and marginal tax burden for each household type . These data on tax burdens and cash benefits are widely used in academic research and the preparation and evaluation of social economic policy-making.