This calculates the years between two dates using the 30/360 day basis convention. This convention assumes that months consists of 30 days and years consist of 360 calendar days.

thirty_360(date1, date2)



A date-time object.


A date-time object.


A numeric value representing the number of years between date1 and date2.


The day count is determined after making the following (ordered) modifications:

  1. If the start date is the 31st, set the start dates to the 30th.

  2. If the start date greater than the 29nd and the end date is the 31st then set the end dates to the 30th.

The year fraction is then calculated as: $$\frac{(d_2 - d_1) + (m_2 - m_1) \times 30 + (y_2 - y_1) \times 30}{360}$$

The order of date1 and date2 is not important. If date1 is less than date2 then the result will be non-negative. Otherwise, the result will be negative.

This is also known as the bond basis.

See also

Other counter methods: actual_360, actual_365, actual_actual_isda, is_valid_day_basis, thirty_360_eu_isda, thirty_360_eu_plus, thirty_360_eu, thirty_360_us, year_frac