R/personal-allowance.R

In ianksalter/uktax: Functions for Calculating UK Tax and Benefits for Economic Analysis

#' The Personal Allowance Class
#'
#' This class describes the personal allowance that a person has in the UK
#' tax system.In the UK the personal allowance is how much you can earn
#' tax free. However the allowance is withdrawn at the given rate over the
#' threshold. Note this is a simplification of the actual UK tax system.
#' For example this class ignores the married couples allowance.
#' @field allowance The amount of the allowance.
#' @field threshold The income at which the allowance starts to be withdrawn.
#' @field rate The rate at which the allowance is withdrawn.
#' @method amount Determines how much personal allowance a person has dependant
#' upon their income.
#' @section Methods:
#' \describe{
#' \item{\code{amount}}{Determines how much personal allowance a person has
#' dependant upon their income.}
#' }
#' @export
#' @examples
#' personal_allowance_2017 <- PersonalAllowance$new(
#'   base = 11500,
#'   threshold = 100000,
#'   withdrawalRate = 0.5
#' )
#' personal_allowance_2017$amount(101000)
PersonalAllowance <- R6::R6Class("PersonalAllowance",
                            public = list(
                              base = NULL,
                              threshold = NULL,
                              withdrawalRate = NULL,
                              initialize = function(base = NA,
                                                    threshold = NA,
                                                    withdrawalRate = NA) {
                                self$base <- base
                                self$threshold <- threshold
                                self$withdrawalRate <- withdrawalRate
                              },
                              amount = function(income) {
                                if (income < self$threshold)
                                  self$base
                                else
                                  max(0,
                                      self$base -
                                        floor(
                                          (income - self$threshold) *
                                            self$withdrawalRate))
                              }
                            )
)


# Data sourced from:
# https://www.gov.uk/government/publications/rates-and-allowances-income-tax/income-tax-rates-and-allowances-current-and-past
personal_allowance_data <-
  tibble::tribble(
    ~year, ~base, ~threshold, ~withdrawalRate,
    #----/------/-----------/----------------
    2016, 11000, 100000, 0.5,
    2017, 11500, 100000, 0.5,
    2018, 11850, 100000, 0.5,
    2019, 12500, 100000, 0.5
  )

personal_allowances <-
  tibble::tibble(
    year = personal_allowance_data$year,
    allowance = purrr::pmap(list(personal_allowance_data$base,
                                 personal_allowance_data$threshold,
                                 personal_allowance_data$withdrawalRate),
                            PersonalAllowance$new)
  )


# TODO: Delete stuff below once refactored.
# Sourced from:
# https://www.gov.uk/guidance/rates-and-thresholds-for-employers-2017-to-2018
# personalAllowance2017 <- PersonalAllowance$new(
#   base = 11500,
#   threshold = 100000,
#   withdrawalRate = 0.5
# )

# Sourced from:
# https://www.gov.uk/government/publications/rates-and-allowances-income-tax/income-tax-rates-and-allowances-current-and-past
# personalAllowance2015 <- PersonalAllowance$new(
#   base = 10600,
#   threshold = 100000,
#   withdrawalRate = 0.5
# )