You can make a Costco Credit Card payment online (through either Citi or Costco), using the Citi mobile app, or by mailing Citi a check or money order. If you decide not to use the mail, you'll have the option of paying your Costco credit card bill with an electronic transfer from a checking account, savings account or prepaid card.

You can choose whichever option is most convenient. And to help you make that determination, we'll explain each payment method in more detail below.

Here's how to make a Costco Credit Card payment:

By mail. Once you receive your statement for the month, you can mail your check or money order payment to Citi at: Citibank / Choice, P.O. BOX 9001037, Louisville KY, 40290-1037. Make sure to postmark it by the day the bill is due. Otherwise, you'll be marked as late.
Citi online. Sign into your account on the Citibank website. Click the “Payments” tab, select “Make A Payment,” and choose a payment to use to complete the transaction.
Costco online. You can pay through the Costco Customer Care website. After you register for an online account, simply log in with your username and password to pay your bill.
Citi mobile app. Citi's free Apple and Android apps offer the same features as the Citi website. Once you download the app and sign in (same username and password as the web version), you'll be able to see and pay your bills.

There are numerous ways to make a Citi Costco Credit Card payment. So just choose whichever method is easiest for you. What you don't want to do is miss payments, as that can seriously damage your credit score.