FX spread % = (mid rate - offered rate) / mid rate x 100. Here is how to get the mid rate, fix the quote direction, and price the spread in dollars.
The FX spread is the gap between the mid-market exchange rate and the rate a provider gives you. Spread % = (mid rate - offered rate) / mid rate x 100. On a $5,000 payment, a 1.0% spread costs $50 before any listed fee. BlindPay quotes show the market rate and the rate after fees side by side, so the spread is visible before you confirm.
The math is easy. Getting it right is not, because most mistakes happen before the formula: a stale mid rate, a quote written upside down, or a fee taken out before conversion.
Key takeaways
An FX spread is the difference between the mid-market rate and the rate you actually get, usually expressed as a percentage of the mid rate. It is how most providers earn money on a currency conversion.
The mid-market rate is the midpoint between the price at which banks are buying a currency and the price at which they are selling it in the wholesale market. Nobody trades at exactly that rate, which is why it works as a neutral yardstick.
The offered rate (also called the final rate or customer rate) is what the provider applies to your payment. The gap between the two is the spread, sometimes called the markup or margin. A separate fee is anything charged on top, such as a flat $25 or a percentage of the amount.
For the wider cost picture, including correspondent fees and receiving bank charges, see hidden fees in international wires and how much cross-border payments cost in 2026.
When you sell one currency to receive another, spread % = (mid rate - offered rate) / mid rate x 100. Both rates must be in the same direction: units of the currency you receive per one unit of the currency you send.
Direction is where most calculations go wrong. Three cases:
One rule handles all three: convert everything to "how much do I receive for one unit I send", then cost % = 1 - (offered / mid). Inverting changes the percentage a little because the base changes. A 1.00% spread measured in BRL per USD shows up as about 1.01% in USD per BRL. The money lost is identical, so pick one convention and stick to it.
Take a live mid rate, align the direction, then compute the percentage and convert it to money. Here it is on a $5,000 payment from USD to BRL.
Assumptions (illustrative, not a live quote or a BlindPay price): mid-market rate 5.4000 BRL per USD, offered rate 5.3460 BRL per USD, no separate fee.
Check it from the recipient's side. At mid, $5,000 buys R$27,000. At 5.3460, it buys R$26,730. The R$270 gap, divided by the 5.40 mid rate, is $50. Same answer, which is the point: if the two methods disagree, one of your inputs is wrong.
A live market data feed gives you a real-time mid rate. Official reference rates are free and public but are set once a day, so treat them as a check on the live number rather than a replacement for it.
| Source | Who publishes it | When it is set | Best use |
|---|---|---|---|
| Live mid from a market data feed or trading screen | Data vendors, banks, FX platforms | Continuously during market hours | Benchmarking a quote you are about to accept |
| WM/Reuters benchmark rates | LSEG | Daily fixings, the best known around 4pm London | Month-end valuation, accounting, contracts that reference it |
| ECB euro reference rates | European Central Bank | Around 16:00 CET on working days, except TARGET closing days | EUR sanity checks; the ECB says the rates are for information only and discourages using them for transactions |
| Banxico FIX | Banco de México | Released from 12:00 on banking days, from an average of wholesale market quotes for settlement two banking days later; published in the Diario Oficial the next banking day | USD/MXN reference for contracts and peso-denominated obligations |
| PTAX | Banco Central do Brasil | Four dealer surveys at random times inside 10:00-10:10, 11:00-11:10, 12:00-12:10 and 13:00-13:10 Brasília time | USD/BRL reference for contracts, tax, and accounting |
Two things to know about reference rates. First, they lag. PTAX is built from surveys that end around 13:10 in Brasília, so by late afternoon the live market can sit well away from it. Second, they are not quotes. Nobody will deal with you at PTAX or the FIX, so a provider quoting a little away from them is not necessarily overcharging.
For stablecoin routes there is one more wrinkle. USDC and USDT trade close to one dollar, but not at exactly one dollar every second. When the quote is in USDC per BRL, compare against the USD mid and accept that a few hundredths of a percent may come from the token, not the provider.
Use the all-in formula: cost % = 1 - (amount received / (amount sent x mid rate)). It folds spread and fees into one number, whatever the provider calls them.
Assumptions (illustrative): $10,000 USD to MXN, mid-market rate 18.50 MXN per USD, so $10,000 is worth MXN 185,000 at mid.
| Quote A: "no fee" | Quote B: fee plus tighter rate | |
|---|---|---|
| Fee | $0 | $30, deducted before conversion |
| Offered rate | 18.13 MXN per USD | 18.40 MXN per USD |
| Spread on the rate | 2.00% | 0.54% |
| Amount converted | $10,000 | $9,970 |
| Recipient gets | MXN 181,300 | MXN 183,448 |
| Shortfall vs mid (MXN 185,000) | MXN 3,700 | MXN 1,552 |
| All-in cost | 2.00%, about $200 | 0.84%, about $84 |
Quote A looks free and costs more than twice as much. That is why fee lines alone tell you very little.
Note the order of operations in Quote B. The $30 is taken before conversion, so the recipient loses the fee at the offered rate, not at mid. Some providers deduct fees from the local currency after conversion instead. The all-in formula doesn't care which. It only looks at what arrives.
The crypto on-ramp fees guide runs the same kind of comparison for the payin side, and stablecoin FX slippage covers the cost that appears after you accept, when the rate you get drifts from the rate you were shown.
Most wrong answers come from bad inputs, not bad arithmetic. Five to check before you trust the number:
Every BlindPay quote shows both rates and every fee line, so you can compute the spread without a separate data feed. The fields come straight from the payout quote response.
| Field | What it is | How to use it |
|---|---|---|
commercial_quotation | The raw market exchange rate | Your market benchmark for this quote |
blindpay_quotation | The rate net of BlindPay's fee | The offered rate in the spread formula |
flat_fee | The flat-fee component | Add it to the all-in cost |
partner_fee_amount | Your own markup, if you passed a partner_fee_id | The margin your platform adds for its users (partner fees) |
sender_amount / receiver_amount | Amount sent and amount received, in minor units | The inputs to the all-in formula |
expires_at | Quote expiry in epoch milliseconds, 5 minutes by default | The window in which the numbers hold |
So BlindPay's FX margin on a quote = (commercial_quotation - blindpay_quotation) / commercial_quotation. To check the market rate itself, compare commercial_quotation with a live mid rate from your own source at the same minute.
For example, a quote with commercial_quotation 5.40 and blindpay_quotation 5.373 carries a 0.5% FX margin (illustrative numbers). Add flat_fee and any partner_fee_amount, and the all-in cost falls out of receiver_amount.
BlindPay quotes use real-time rates and lock rate and fees for the quote's lifetime, so the spread you calculate is the spread you get if you execute before expires_at. Payouts settle over Pix and SPEI in minutes, and over ACH, SEPA, and SWIFT (POBO/COBO) on the rail's schedule (cut-off times). There is no pre-funding: the quote is funded when you execute it.
Plans are published on the pricing page. Per-transaction costs show up in each quote rather than in a rate card, which is why the fields above matter.
Pull one real quote for your main corridor, take a live mid rate at the same minute, and run both formulas: spread % on the rate, then the all-in cost % on the amount received. If you are building on BlindPay, create a test quote from the payout quickstart and compute the margin from commercial_quotation and blindpay_quotation. Then read what real-time cross-border settlement is to see where the rate fits in the rest of the payment.
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