PTAX

PTAX is the official exchange rate published daily by the Brazilian Central Bank (Banco Central do Brasil, BCB). It is the reference rate used in financial contracts, tax reporting, and regulatory filings in Brazil.

Quotes are fetched from the BCB's exchange rates page and represent the closing bid and ask rates for each currency pair against the Brazilian Real (BRL). The rate exposed by this library is the mid-point between those two quotes.

Installation

Add PTAX to your project's dependencies in mix.exs:

# mix.exs
def deps do
  [
    {:ptax, "~> 2.1"}
  ]
end

PTAX starts its own isolated retriever, so ex_money's default auto-started retriever isn't needed. Turn it off:

# config/config.exs
config :ex_money, auto_start_exchange_rate_service: false

See ex_money's exchange rates service docs for details.

In scripts and Livebook notebooks, pass the same config to Mix.install/2:

Mix.install(
  [{:ptax, "~> 2.1"}],
  config: [ex_money: [auto_start_exchange_rate_service: false]]
)

Usage

Convert using the latest known rates

iex> PTAX.exchange(Money.new!(:USD, "100"), :BRL)
{:ok, %Money{}}

iex> PTAX.exchange!(Money.new!(:USD, "100"), :BRL)
%Money{}

The lookup automatically walks back up to 7 days to find the most recent available data.

Convert using rates for a specific date

iex> PTAX.exchange(Money.new!(:GBP, "50"), :BRL, ~D[2026-05-15])
{:ok, Money.new!(:BRL, "337.63")}

iex> PTAX.exchange!(Money.new!(:GBP, "50"), :BRL, ~D[2026-05-15])
Money.new!(:BRL, "337.63")

Dates with no BCB data (weekends, holidays) return {:error, reason} or raise with the bang variants:

iex> PTAX.exchange(Money.new!(:USD, "100"), :BRL, ~D[2025-12-25])
{:error, {Money.ExchangeRateError, "no exchange rates available for 2025-12-25"}}

iex> PTAX.exchange!(Money.new!(:USD, "100"), :BRL, ~D[2025-12-25])
** (Money.ExchangeRateError) no exchange rates available for 2025-12-25

Using PTAX rates with ex_money

PTAX runs as an isolated, named ex_money retriever (PTAX.Retriever), so it never interferes with any other ex_money retriever your application runs — you're free to use other providers for other currencies alongside it.

To reach ex_money's richer operations (arbitrary conversions, cross rates) with PTAX data, fetch rates from PTAX.Retriever and pass them to any ex_money function that accepts a rates map:

rates = Money.ExchangeRates.Retriever.latest_rates(PTAX.Retriever)
Money.to_currency(Money.new!(:USD, "100"), :BRL, rates)

historic = Money.ExchangeRates.Retriever.historic_rates(PTAX.Retriever, ~D[2026-05-15])
Money.to_currency(Money.new!(:GBP, "50"), :BRL, historic)

See also

• Money.to_currency/2,3 — convert between any two currencies
• Money.cross_rate/2 — derive a cross rate between two currencies
• Money.ExchangeRates.Retriever — the retriever process and its named-instance functions