On the surface, the deal making PayPal and Dwolla payment options on Pay.gov, the US Treasury’s online payments hub, looks massive — trillions-of-dollars massive.

After all, the US Treasury reports that the federal government processed $3.73 trillion (with a T) in fiscal year 2014, 98% of which was settled electronically. Pay.gov processed about $110 billion of that in 100 million transactions.

But looks, or really numbers, can be deceiving, or at least my math implies as such.

Of course, PayPal and Dwolla are not going to be responsible for all 100 million or so Pay.gov transactions in FY 2015, nevermind the fact that 19 government departments need to adopt the new payment options, and that will take time. Pay.gov currently offers two payment options: pay via bank account using ACH or via credit or debit card. According to Dwolla officials, Dwolla and PayPal will be added as payment options to Pay.gov.

It is hard to estimate what percentage of Pay.gov payments will use the Dwolla-or-PayPal options once they are fully adopted. According to some evidence, consumers opt for PayPal over other online payment options one in six times. This data point is wholly unscientific, and even if true, cannot be blindly applied to Pay.gov. However, for s**** and giggles, let’s say that ratio is about right and around 17% of transactions will equally run through either Dwolla or PayPal. (Yes, I know it won’t be absolutely equal, but stay with me here.)

In sum, Dwolla and PayPal could each process 8.35 million transactions with a face value of $9.2 billion. Now, here is where things diverge. Dwolla states that it charges $0.25 per transaction, assuming the transaction is for more than $10, otherwise Dwolla charges nothing. PayPal, meanwhile, charges $0.30 per transaction and 2.9% of the face value of the transaction. Therefore, according to my math, Dwolla stands to generate $2.1 million of revenue from Pay.gov, while PayPal could generate … wait for it … $268.9 million.

I have reached out to Bureau of the Fiscal Service, the unit within the US Treasury that manages Pay.gov, for confirmation that PayPal and Dwolla are free to charge their own settlement rates. I am still waiting for confirmation, but the preliminary conversation I had with the bureau suggested that indeed PayPal and Dwolla have pricing freedom.

Admittedly, this is all back-of-the-envelope analysis, so take it with a hefty grain of salt. But there is a takeaway here — which is that the Pay.gov deal will likely have vastly different financial implications for Dwolla and PayPal.

Learn more about alternative payments at Bank Innovation 2015, March 2-3 in Seattle. Click here to get invited.