This calculates the years between two dates using the Actual/Actual ISDA day basis convention. This convention counts the number of calendars between the start and end dates. The definition of a year is contingent on whether the year is a leap year or not. The year fraction is calculated as: $$ \frac{d_1}{{dy}_1} + \frac{d_2}{{dy}_2} + y_2 - y_1 - 1 $$

actual_actual_isda(date1, date2)

date1 | A date-time object |
---|---|

date2 | A date-time object |

a numeric value representing the number of years between
`date1`

and `date2`

.

where:

\(d_1\) is the remaining days in the first date's year including both the start and end date

\(d_2\) is the number of days to the second date from the start of that year

\({dy}_1\) is 366 if the first date is in a leap year. Otherwise it is 365

\({dy}_2\) is 366 if the second date is in a leap year. Otherwise it is 365

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.

Other counter methods: `actual_360`

,
`actual_365`

,
`is_valid_day_basis`

,
`thirty_360_eu_isda`

,
`thirty_360_eu_plus`

,
`thirty_360_eu`

, `thirty_360_us`

,
`thirty_360`

, `year_frac`