PTAX is the Central Bank of Brazil's published average of dealer quotes for the real against the dollar, and it is the right number to write into a contract, but a payout cannot settle at it. A payout needs a price someone will trade at, and PTAX is computed from quotes that are already in the past. The working rule is short: use PTAX to fix the reais amount a contract says is owed, and use a live quote to move the money.
Best for: treasury and finance teams that pay Brazilian suppliers or contractors in reais from a USDC balance and have to explain why the payout rate differs from the rate on the invoice.
The confusion shows up at payment time. An invoice says "converted at PTAX", the payout quote shows another rate, and someone in finance asks which one is right. Both are, because they answer different questions. The margin inside a quote is covered in how stablecoin payout pricing works, so this post stays on the rate itself.
What PTAX is, and the rule behind it
PTAX is the name of the real-dollar rates that the Central Bank of Brazil (BCB) calculates and publishes every business day. It is built from consultations with the dealers that are accredited to trade foreign currency with the BCB. In each consultation every dealer must give a buy quote and a sell quote for the interbank spot market, for settlement in two business days (D+2), and the quotes cannot be withdrawn after the consultation window closes. The BCB drops the two highest and the two lowest quotes on each side and averages the rest.
The rule is BCB Resolution 45 of November 24, 2020, in force since January 1, 2021. It replaced Circular 3,506 of September 23, 2010, along with two circulars that amended it, so any text still citing the 2010 circular describes a superseded rule.
The resolution fixes four consultations a day, two minutes each, with a random start inside these windows:
Consultation | Start window (Brasília time) |
First | 10:00 to 10:10 |
Second | 11:00 to 11:10 |
Third | 12:00 to 12:10 |
Fourth | 13:00 to 13:10 |
Each result is published right after calculation and validation. The PTAX of the day is the arithmetic mean of the four results, buy and sell kept apart, published together with the last one. That makes PTAX a lunchtime number: on a normal day it exists at about one in the afternoon. On days with different interbank hours, the BCB tells dealers the schedule in advance.
Five bulletins a day, and what one real day looked like
The BCB publishes five dollar bulletins per date: one opening, three intermediate and one closing, which the system calls "Fechamento PTAX". The closing bulletin is what people mean by "PTAX". This is October 28, 2026, read from the BCB's PTAX service on October 29, 2026:
Dollar bulletins published by the BCB for October 28, 2026, in reais per dollar.
Bulletin | Published (Brasília time) | Buy | Sell |
Opening | 10:11 | 5.3233 | 5.3239 |
Intermediate | 11:07 | 5.3131 | 5.3137 |
Intermediate | 12:05 | 5.3621 | 5.3627 |
Intermediate | 13:05 | 5.3672 | 5.3678 |
Closing (PTAX) | 13:05 | 5.3414 | 5.3420 |
The four sell results average to 5.3420, the closing PTAX sell rate, so the arithmetic in the resolution is visible in the data. The table also shows how little a daily average says about the price at a given minute. Between the 11:07 and the 13:05 bulletins the sell rate rose from 5.3137 to 5.3678, just over 1%, which is BRL 541 on USD 10,000 in two hours. The closing PTAX of 5.3420 sits between the two, and nobody could have converted at it at either time.
Why a payout cannot settle at PTAX
A payout is a trade, and a trade needs a counterparty who has agreed to a price before the money moves. PTAX fails that test three ways.
It arrives after the fact. A payout instructed at nine in the morning cannot reference the day's PTAX, and one instructed at three in the afternoon can only reference it in hindsight.
It is built for D+2 settlement. Dealers quote the interbank spot rate for settlement two business days later, while a Pix (Brazil's instant payment system, run by the Central Bank) payout lands in seconds. The rate for it is a different instrument from the one PTAX averages.
It exists on business days only, while Pix runs every day of the year. A payout on a Sunday has no PTAX of its own.
A fixing order, where a dealer commits to fill you at a benchmark and carries the difference, is a wholesale FX product with its own price. A provider that settled every transfer at PTAX would be taking the market risk of the whole day on your behalf, without being paid for it.
When PTAX is the right reference
PTAX is the right rate when two parties need the same number after the event and neither can dispute it. The BCB publishes it for anyone, so a supplier in São Paulo and a payer in Austin get the same answer.
That makes it the natural choice for the clause of a contract or invoice that converts a dollar amount into reais: "the amount in reais equals the invoice value in dollars times the PTAX sell rate of the invoice date". It also fits a policy that needs one named rate per day to compare executions against. The clause only works when it names the side, the bulletin and the date, because the BCB publishes ten rates for each date. This post covers rate mechanics only. Whether a transaction must be reported at a particular rate for tax or accounting is a question for your advisers.
When a live quote is the right rate
A live quote is the right rate every time money moves. It is the price at which your specific payout executes, for your amount and rail, with the provider's margin inside it, valid for a stated window. It tells you what leaves the wallet and what lands in the supplier's bank account.
There are two kinds, and the choice follows the flow. A floating quote is a real-time reference with no lock and no fee, and the rate applied at execution can differ slightly, so it fits showing an estimate on screen. A locked quote holds the rate for 30 seconds, 1 minute or 5 minutes, takes either a source or a target amount, and returns an expiry. The 30-second lock carries no fee, and the longer ones include a fee that covers volatility. Software can run on the 30-second lock, and a payout a person reviews before approving may need a longer one.
The corridor is explained in what a stablecoin corridor is, and the two directions of the pair are on the USDC to BRL and BRL to USDC pages.
One payment, two rates
Most invoices need both. The contract sets the reais amount with PTAX, and a locked quote that takes the reais amount as its target solves for the USDC to send, so the supplier receives what the contract says.
I would write the contract clause so that it names the PTAX side, the bulletin and the date, and I would keep the executed quote in the same file as the invoice. A clause that only says "PTAX" starts an argument the first time the payout differs from the invoice, and the argument is about wording nobody can check afterwards. I would also never ask a payout provider to settle at PTAX. A provider that agreed would carry a day of market risk for you and charge for it somewhere you could not see, which is worse than a quote you can read.
A worked example: a USD 50,000 invoice paid in reais
A Brazilian supplier invoices USD 50,000, and the contract converts it at the PTAX sell rate of October 28, 2026, the invoice date. The fix is real, taken from the table above. The quote on payment day is an illustration, with round rates that are not a Lumx price and not a forecast.
Step | Calculation | Result |
Reais owed under the contract | 50,000 x 5.3420 | BRL 267,100.00 |
USDC implied by the PTAX | 267,100.00 / 5.3420 | 50,000.00 |
USDC at an illustrative base rate of 5.3350 | 267,100.00 / 5.3350 | 50,065.60 |
USDC at an illustrative final rate of 5.3250 | 267,100.00 / 5.3250 | 50,159.62 |
Market movement since the fix | 50,065.60 minus 50,000.00 | 65.60 |
Execution cost, fees included | 50,159.62 minus 50,065.60 | 94.02 |
The example treats one USDC as one dollar, which keeps the arithmetic clean. In practice USDC trades close to a dollar and not exactly at it, and that small basis is part of the gap you will see.
Of the 159.62 USDC gap, 65.60 is the market moving between the fix and the quote, which no provider controls. The other 94.02 is the cost of executing, and it is the part to compare across providers. The split needs two rates from the same quote, the base rate before fees and the final rate after them, which is why a quote that shows only one number cannot be reconciled against a fix.
To reconcile later, store a few fields for each payout when it runs: the PTAX clause with the rate read from the BCB, the reais amount it produced, the quote id with its base rate, final rate and fee lines, the expiry and submission times, and the USDC sent. Over a month, a movement column that swings both ways and a cost column that does not is a normal picture, and a cost column that drifts upward is the one to raise with the provider.
When a PTAX contract with a live payout is the wrong tool
A rate fixed weeks before payment. A locked quote protects the minutes between pricing and paying, not the weeks between the invoice date and the payment date. That exposure comes from how the contract is written, and a treasury policy or a bank hedge is the tool for it.
A contract that names no benchmark. With a negotiated rate or a plain reais amount there is nothing to reconcile against, and a monthly variance report has no reader.
Small payouts. On a few hundred dollars the flat fees outweigh the movement and execution split, so keep one line per small payout and run the full reconciliation on the large ones.
What a BRL payout looks like on Lumx
Lumx is stablecoin payments infrastructure for businesses that move money between Latin America and the rest of the world: one API to collect, hold, convert, and pay out in BRL, MXN, COP, USD, EUR, and GBP or in USDC and USDT, over local rails such as PIX, SPEI, PSE, Bre-B, ACH, FEDWIRE, SEPA, and Faster Payments, with SWIFT and on-behalf-of payments and collections (POBO and COBO) in USD, EUR, and GBP, plus named virtual accounts, custodial wallets, and KYB/KYC built in.
A BRL payout on Lumx is a live quote followed by an off-ramp over Pix. The paying company asks for a locked quote from USDC to BRL, passing either the USDC to send or the reais to deliver. The response carries an expiresAt, the base and final rates, and the fee lines for Lumx and for any partner fee the platform adds. The company then submits the off-ramp with the quote's id, and the payout converts at the quoted rate. The rate is not PTAX, and the PTAX clause in the contract stays what it was: a number the finance team reads from the BCB and holds beside the quote.
For the contract case in this post, quote with the reais amount as the target. The supplier receives the amount the clause produced, and the USDC cost is whatever the quote returns. The payout runs from the paying company's custodial wallet, and Pix has no cut-off in the documentation, so a Sunday payout executes on Sunday. The path from a wallet to a Brazilian bank account is in sending USDC to Brazilian banks, and the reverse leg, collecting reais into USDC, is in converting BRL to USDC for treasury.
Failures return codes. A quote used after its window returns EXCHANGE_RATE_EXPIRED, and the answer is a new quote, not a retry of the old one. A transaction held for review shows as an RFI (request for information, a compliance hold that asks for a document before a transaction clears), and webhooks report each status change. Pricing is a monthly platform fee plus usage-based fees, with transparent FX on locked quotes and no pre-funding. What providers publish for pricing is compared in stablecoin API pricing compared, BRL is part of the Lumx coverage, and the flow end to end is on the global payments page. For the dollar side, start with what USDC is.
Methodology and sources
The PTAX rule was read from the text of BCB Resolution 45 of November 24, 2020 and from the superseded Circular 3,506 of September 23, 2010, both served by the BCB's normative API on October 29, 2026. The BCB's normative pages are a JavaScript application, so the API record is the version that returns the text. The resolution was not marked as revoked or amended in that record.
The bulletins for October 28, 2026 come from the BCB's PTAX open data service, read on October 29, 2026, through its daily bulletins query for USD. The average of the four sell results was computed here from those figures and matches the closing sell rate.
Product behavior comes from the Lumx documentation on exchange rates, the exchange rate API reference, error codes and payment rail cut-off times, all read on October 29, 2026. The reais and USDC figures in the worked example are arithmetic on the October 28 PTAX sell rate and on assumed round rates, which are marked as illustrative. No live Lumx quote was pulled for this post. Tax and accounting treatment was not researched and is outside the scope.
Verified on October 29, 2026. Operational context, not legal, tax, or investment advice.
Cover photo: Guilherme Braga on Unsplash.
What is PTAX?
PTAX is the set of real-dollar buy and sell rates that the Central Bank of Brazil calculates every business day from four consultations with accredited dealers. The PTAX of the day is the average of the four results, published with the last one around one in the afternoon. It is a reference for contracts, not a price you can trade at.
Can I pay a supplier at the PTAX rate?
You can write PTAX into the contract, and the contract then sets the reais amount. The payout itself converts at a live quote, because PTAX is published after its consultations close and nobody executes a transfer at it by default. The usual setup is to fix the reais amount with PTAX and ask for a quote whose target is that amount.
When is PTAX published?
The BCB runs four consultations between 10:00 and 13:10 Brasília time on business days, and publishes each result after calculation and validation. The PTAX of the day comes out with the fourth one, so on a normal day it is known shortly after 13:00. On days with different interbank hours the BCB announces the schedule to dealers beforehand.
Why does my payout rate differ from PTAX?
Two things move it. The market changes between the PTAX consultations and the moment the quote is issued, and the quote carries the provider's margin and fees. Store the quote's base rate and final rate next to the PTAX figure, and the gap splits into those two parts.
How long does a Lumx locked quote last?
A locked quote can be held for 30 seconds, 1 minute or 5 minutes. The 30-second lock has no fee, and the longer ones include a fee that covers volatility. If the lock expires before the transaction is submitted, the quote id is no longer valid and you request a new one.
