Cross-selling
Offering a customer a different, related product alongside or after the one they buy, such as a case with a phone or insurance with a mortgage. It increases basket size and ties the customer to more of the range, which tends to improve retention. Recommendations work when the products are genuinely used together; random 'you may also like' offers mostly teach people to scroll past them.
Where it's used
Used on e-commerce product pages and checkouts, in banking, telecoms and retail staff training. Good when purchase data shows which products are bought together, so the offer matches what customers already do.
How to calculate it
Average order value = total revenue ÷ number of orders
Worked example
Illustrative numbersAn online camera shop gets 2,000 orders a month with an average order value of $60. It adds a $15 memory card offer at checkout, and 12% of orders include it.
Orders with the add-on
2,000 orders × 12% = 240
Add-on revenue
240 cards × $15 = $3,600
New average order value
(2,000 orders × $60 + $3,600) ÷ 2,000 orders = $61.80
What it tells you
A 12% attach rate adds 3% to the average order. The offer works because nobody wants a camera without a memory card.