Buy-now-pay-later at checkout has become standard. Shop Pay Installments (powered by Affirm) is Shopify’s first-party version, and most merchants enable it without thinking too hard. Sometimes it’s a clear win. Sometimes it’s a tax on your margin. Here’s how to tell which one you’re paying.
How it works in 2026
Customers see a “Pay over time with Shop Pay Installments” option at checkout when their cart total is between roughly $50 and $20,000. They get a soft credit pull, choose a plan (4 interest-free biweekly payments, or 3–24 months with interest), and complete checkout.
The merchant gets paid in full immediately. The fee is 5–6% of the order total (varies by plan and merchant size).
When it’s a clear win
Average order value > $200. The math works because Affirm’s fee is offset by larger basket sizes when customers can spread the cost. We’ve seen AOV jump 20–35% on furniture, jewellery, electronics, and bike stores after enabling it.
Considered purchases. Customers research, compare, deliberate. Removing the lump-sum sticker shock at the moment of decision is what BNPL is for.
Younger demographic. Gen Z and millennials are more comfortable with installments than older customers. If your customer base skews under 35, BNPL adoption is much higher.
When it costs you more than it earns
AOV < $80. A 5–6% fee on a $60 order is real money you’d have got anyway. Customers buying $60 items rarely need installments — they’re not deliberating, they’re impulse buying.
High repeat-rate, low margin. Subscription stores, consumables, low-cost beauty: customers know what they want, the basket is small, the fee compounds across a year of orders.
B2B / wholesale. B2B buyers don’t use BNPL. Enabling it just adds clutter to the checkout.
The middle case
AOV between $80 and $200, mixed customer demographics. This is most stores. The fee might exactly offset the AOV lift. You won’t know until you test.
How to test: turn it on for 30 days. Compare AOV, conversion rate, and total revenue to the prior 30. Make sure traffic mix is comparable (a quiet vs. busy month will lie to you).
A counterintuitive risk
Stores that introduce BNPL sometimes see no AOV change — but their customer mix shifts toward installment buyers. That’s fine until 6 months later when your accounts receivable through Affirm starts having default issues. The fee covers Affirm’s risk, not yours, but the customer experience hits you when collections happen.
For most merchants, this is a non-issue. It does mean: if your sales spike disproportionately on Installments, look at refund and chargeback rates as a separate KPI.
How to position it on the storefront
If you’ve decided it’s right for you, lean in:
- Show the “as low as $X/mo” line on the product page, not just at checkout. This is where it earns AOV.
- Use the official Shop Pay Installments pricing widget — it’s compliant and looks credible.
- Don’t reach for it as a discount substitute. Discounts attract a different customer than installments.
The honest answer
For DTC stores selling products in the $200–$2000 range, Shop Pay Installments is one of the highest-ROI features Shopify ships. For stores under that band, it’s a vanity feature that costs you margin.
The fee is real. Treat it like a marketing channel: measure the lift, decide if you’d buy it as media at that price, and turn it off when the maths stop working.