Welcome bonuses on cards and accounts are large enough to look uneconomic. The spending condition attached to them is what makes the arithmetic work for the issuer.
What the bonus is buying
Acquiring a customer costs money in advertising, application processing and identity checks whether or not the account is ever used.
A bonus converts that spend into a payment made only on success. Nothing is paid unless an account opens and reaches a defined level of activity.
It is therefore best read as an acquisition cost the issuer expects to recover over the life of the relationship, rather than as a discount on anything.
Why a threshold rather than a flat gift
A flat gift would attract people who open the account, take the money and never use it. That group costs the issuer everything and returns nothing.
Requiring spend within a window filters for customers who will actually put the card to work, since only genuine usage reaches the figure.
The window also compresses the behaviour into a period short enough to establish a habit, which is the real objective behind the design.
How the threshold is calibrated
The figure is set above typical natural spending for the target segment, so meeting it requires deliberately routing purchases through the new card.
Set too low and the issuer pays out to people who change nothing. Set too high and applications fall away, so the number sits between those failure modes.
A share of applicants will miss it entirely. That group covers part of the cost of the bonuses paid to everyone who succeeded.
The conditions that quietly matter
Qualifying spend usually excludes balance transfers, cash withdrawals, gambling, and payments the issuer treats as cash equivalents.
The clock typically starts at account opening rather than at card activation, so delivery delays eat into a window that was already fixed.
Refunds reduce the running total after the fact, which can pull an account back below the threshold weeks after the purchases were made.
Where the offer stops being worthwhile
Spending that would not otherwise have happened costs more than the bonus returns in almost every case, because the bonus is a fraction of the outlay.
Timing the application around expenditure already committed avoids that trap, since the threshold is then met by spending that was going to occur regardless.
Issuers anticipate this with eligibility rules excluding recent or previous holders, which is why the same offer is not available repeatedly to the same person.