Periods, Instants

Most of the values calculated in OpenFisca, such as an income tax, or a housing allowance, can change over time.

In simulations, parameters and variables, OpenFisca handles time via periods and instants.

• Instant: the atomic unit is a day, so instants are day dates.

Example: the 15th June 2015.

• Period: a succession of days.

Example: a month (“July 2015”), a year (“2015”), several months (“July and August 2015”) or the eternity.

The smallest unit for OpenFisca periods is the month. Therefore:

• All periods are presumed to start on the first day of their first month.
• A period cannot be smaller than a month.

The largest unit for OpenFisca periods is the eternity, which is used for variables that are constant over time, e.g. a date of birth.

Read more about the periods implementation in OpenFisca