How Amazon defines it
The look-back window is 365 days. If a shopper bought from your brand 364 days ago and buys again today through your ad, the order is not new-to-brand. If the gap is 366 days, it is. The seven sub-metrics break the count down by orders, sales, units, and percentages — so you can isolate which campaigns, audiences, and ASINs drive net-new acquisition versus re-purchase.
Why it should anchor the JBP media commitment
Most brands negotiate JBP media spend against ROAS or ACoS. That's a campaign-efficiency conversation. NTB is an acquisition conversation — the one CPG executives actually care about, because new-customer counts feed into category share growth, distribution wins, and DTC retargeting (NTB-acquired customers can be loaded into Amazon DSP audiences and matched against your CRM in AMC). A media commitment built around an NTB target gives both sides — Amazon and the brand — something measurable that ties to commercial growth, not just incremental sales.