An advertisement distribution system can log advertisement conversions using Near Field Communication (“NFC”). An online advertisement may be served to a user in response to a query or at a website. In response to the user selecting the advertisement, a landing page is displayed to the user and information regarding the advertisement is stored for logging purposes. The landing page may instruct the user to check in with an NFC-enabled device at an NFC base station of a merchant. The NFC base station transmits information identifying the merchant to the user's device and, in turn, the user's device transmits the information to the advertisement distribution system. The advertisement distribution determines that the advertisement resulted in a conversion using information regarding the advertisement and the information identifying the merchant received from the NFC base station via the user's device.