Terms suggest that there is no expiration date and that there is no max. Seems too good to be true.

“For every $100 in IKEA gift cards purchased online from IKEA US in a single transaction, you’ll receive a free $20 IKEA eGift card delivered via email to the email address associated with your purchase as a special thank you. Sales tax, shipping or other charges will not count towards the qualifying $100. Limited time offer, valid only for online gift card purchases made November 24 to November 27, 2017 11:59PM EST. Offer only valid for IKEA US. Not valid on previous purchases or for cards purchased in-store. May not be combined with any other offer. No cash value. Gift cards subject to additional Terms and Conditions. Not for resale. No substitutions. Not transferable. Cancellations of gift card orders prior to delivery may result in forfeiture of the free eGift card. Void where prohibited by law.”