user67917: I'd like to determine what trading fees to expect before placing an order.
According to https://www.bitstamp.net/fee_schedule/ Bitstamp's trading fees depend upon the USD total of a customer’s last 30 days worth of transactions.
How can one calculate this amount using the Bitstamp API? It doesn't seem to be possible.

user43135: Those are Bitstamp trading fees, not Bitcoin transaction fees. Trading fees are automatically calculated and deducted by Bitstamp when executing a trade.
For choosing the right Bitcoin fee, use bitcoin-cli estimatesmartfee or one of the many web services.

user41755: Every exchange has a predetermined fee structure for any financial transaction that you perform on the exchange. Also this fee is subject to the volume you have traded.
From the links you have provided, the API documentation page contains the user transactions section which would return the list of all transactions you have done. 
You can filter out the last 30days transactions and get the USD volume from that.

user29532: From the API documentation available at https://www.bitstamp.net/api/
The private endpoint https://www.bitstamp.net/api/v2/balance/ includes the fees for all pairs.
The private endpoint https://www.bitstamp.net/api/v2/balance/{currency_pair}/ includes the fee for the specified pair.

67917: <p>I'd like to determine what trading fees to expect before placing an order.</p>

<p>According to <a href="https://www.bitstamp.net/fee_schedule/" rel="nofollow noreferrer">https://www.bitstamp.net/fee_schedule/</a> Bitstamp's trading fees depend upon the USD total of a customer’s last 30 days worth of transactions.</p>

<p>How can one calculate this amount using <a href="https://www.bitstamp.net/api/" rel="nofollow noreferrer">the Bitstamp API</a>? It doesn't seem to be possible.</p>
 43135: <p>Those are Bitstamp trading fees, not Bitcoin transaction fees. Trading fees are automatically calculated and deducted by Bitstamp when executing a trade.</p>

<p>For choosing the right Bitcoin fee, use <code>bitcoin-cli estimatesmartfee</code> or one of the many web services.</p>
 41755: <p>Every exchange has a predetermined fee structure for any financial transaction that you perform on the exchange. Also this fee is subject to the volume you have traded.</p>

<p>From the links you have provided, the API documentation page contains the user transactions section which would return the list of all transactions you have done. 
You can filter out the last 30days transactions and get the USD volume from that.</p>
 29532: <p>From the API documentation available at <a href="https://www.bitstamp.net/api/" rel="nofollow noreferrer">https://www.bitstamp.net/api/</a></p>

<p>The private endpoint <code>https://www.bitstamp.net/api/v2/balance/</code> includes the fees for all pairs.</p>

<p>The private endpoint <code>https://www.bitstamp.net/api/v2/balance/{currency_pair}/</code> includes the fee for the specified pair.</p>
