45% of all Amazon.com Inc.’s U.S. customers, roughly 40 million consumers, belong to the online giant’s Amazon Prime two-day shipping and loyalty program, according to a new report from market research firm Consumer Intelligence Research Partners LLC. That’s up from 29 million at the end of September. Some 3 million holiday shoppers taking trial memberships helped push those Prime numbers higher, according to the report, which also includes estimates related to Kindle devices and the Amazon Visa payment card.

“Amazon Prime membership increased significantly in the holiday quarter,” says Josh Lowitz, partner and co-founder of Consumer Intelligence Research Partners.

The market research firm says Prime members spend on average $1,500 per year, 140% more than the $625 spent annually by other Amazon customers. That’s a 25% increase from last year, when Morningstar Inc. and Consumer Intelligence Research Partners estimated the average Prime member spent $1,200 annually, including the then-$79 membership fee, compared with $600 for the average non-Prime Amazon customer.

Amazon, No. 1 in the Internet Retailer 2014 Top 500 Guide, has since raised the price of Prime to $99 (though the e-retailer offered a $72 sale over the weekend). Households can share Prime memberships—and consumers can take free trial memberships—which also includes access to thousands of movies, TV shows, songs and other entertainment and media titles. Amazon did not immediately respond today to a response for comment about the latest Prime estimates. Amazon is scheduled to report its fourth quarter and full year 2014 earnings on Thursday.

Amazon shies away from being specific about Prime members, opening the door for various independent estimates. A handful of Amazon observers today—not all of them willing to publicly comment on another firm’s Amazon estimates—deemed the new estimate reasonable, however.

The Consumer Intelligence Research Partners also finds:

• 39% of U.S. Amazon customers own Kindle e-readers or tablets (but not those who only use the Kindle mobile apps). Those customers are lucrative given that they spend about $1,450 with Amazon annually compared with $725 for customers without Kindle devices.

• 7% of Amazon customers own Kindle Fire TV boxes or sticks.

• Less than 1% of Amazon customers own Amazon Fire smartphones.

In related news, Amazon today also says it has tweaked the free shipping offered to consumers, including those who buy from sellers on Amazon who do their own fulfillment and who also offer free shipping. Those consumers will now find it easier to meet the $35-mininum order threshold to receive free shipping from such transactions, an Amazon spokesman says. That’s because consumers can combine orders to receive free shipping.

“For example, a customer wants to buy a $25 coffee grinder fulfilled by Amazon. Previously the customer would have needed to find another Amazon-fulfilled item for at least $10 in order to qualify for free shipping on the entire order,” the spokesman says. “Now, seller-fulfilled offers with free shipping can be combined with Amazon-fulfilled offers to meet the $35 order minimum. If the customer adds a $10 bag of coffee sold by a seller with free shipping, the combined price of the grinder and the coffee allows the entire order to qualify for free shipping.”