Instead, their limits change from month - to - month and are typically determined by the card owner's income and past spending habits. (creditdonkey.com)
Card issuers will actually set a spending limit for each cardholder based on certain criteria like income, payment history, past spending patterns, etc.. (rewardexpert.com)
For one thing, many cards that allow you to go past your spending limit without a fee will require you to pay off any excess charges before the end of the billing cycle. (cardrates.com)