Note that you only get BAL for trading on Ethereum Main Net, not on Polygon.
Every eligible trade made through the Balancer Exchange Proxy, results in some BAL being allocated to the address (EOAs only) that sent the transaction. An eligible trade is a swap containing one or more eligible tokens (you can check our whitelisted tokens 👉 here).
Claims are made available on Wednesday (UTC time) following the end of the weekly period (Monday, 00:00 UTC) in which the trade occurred. If you are eligible, you can claim your BAL tokens on claim.balancer.fi.
The amount of BAL awarded to a trade is a function of the number of eligible swaps in the trade (N), which determines a number of gas units (G), the median gas price  of the block the transaction was included in (M), and the BAL/ETH price provided by the CoinGecko closest to the block time (P).
The amount of BAL to be received by the user, is computed as
This program only partially covers gas costs (with very specific caps to prevent attempts at gaming the system), doesn’t cover trading fees, and does not incentivise wash trading.
Estimates are provided on the UI, but actual values are computed off-chain weekly using an open source script, so that any suspicious activity can be filtered out.