The verdict in three sentences
On a 3G connection, a heavy checkout bleeds conversion before the user even pays. Each extra second of delay costs about 7 % of conversion, and each third-party script adds 100 to 400 ms. The target: a checkout under 250 KB and 2 seconds, with an LCP under 2.5 s.
The checkout performance budget
A performance budget sets measurable ceilings. You cut everything that exceeds them.
| Item | Typical heavy page | Optimized target 2026 | Lever |
|---|---|---|---|
| Total weight | 1.8 MB | < 250 KB | WebP images, tree-shaking |
| Third-party scripts | 6 to 9 | 0 to 2 | Remove chat/pixels at checkout |
| Render time (median 3G) | 4.5 s | < 2 s | Inlined critical CSS |
| LCP | 4.8 s | < 2.5 s | Preload the key element |
| HTTP requests | 60+ | < 20 | Bundling, sprites |
| Custom fonts | 3 weights | 1 or system | font-display swap |
Median 3G throughput in Lagos remains modest in 2026: targeting 2 seconds means deferring analytics, removing chat widgets on the payment page and inlining critical CSS.
Every third-party script has a cost
| Third-party script | Average cost (ms, 3G) | Needed at checkout? |
|---|---|---|
| Ad pixel | 150 to 300 | No — defer |
| Live chat widget | 200 to 400 | No — remove |
| Heavy analytics | 100 to 250 | Defer after payment |
| Synchronous A/B testing | 150 to 350 | Load async |
| External fonts | 100 to 200 | Reduce / system |
| Payment SDK | 80 to 150 | Yes — keep, slim down |
At checkout you keep only the essentials: the payment SDK. Everything else waits for the confirmation page.
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Mini case study
Chidi, who runs a fashion shop in Lagos, had a 1.8 MB checkout loading in 4.5 s on 3G, with a 2.1 % conversion on 8,000 visits/month, or 168 orders. Moving under 250 KB and 2 s (−2.5 s delay ≈ +17 % conversion), he reaches 2.5 %, or 200 orders. With an average basket of NGN 18,000, that is 32 orders × 18,000 = NGN 576,000/month gained just by slimming the page.
FAQ
What does one second of delay really cost? About 7 % less conversion per second on mobile. On slow 3G, going from 4.5 s to 2 s can mean +15 to +18 % conversion.
Do you really have to remove chat at checkout? Yes. A chat widget adds 200 to 400 ms and distracts from the purchase. Re-enable it on the confirmation or support page, not on payment.
What page weight should you target on 3G? Under 250 KB to hold 2 seconds. That requires WebP/AVIF images, inlined critical CSS and zero non-essential scripts.
Is LCP the right metric? Yes, aim for an LCP under 2.5 s: it is the moment the main content (pay button, amount) becomes visible. That is what the buyer perceives as "the page is ready".
How do you defer analytics without losing data? Load analytics scripts after the payment event or via requestIdleCallback. You keep measurement without penalizing the initial render.
Let's talk about your project. We audit your checkout weight and bring it under 250 KB and 2 seconds. WhatsApp +221 77 596 93 33.
Mohamed Bah
Fondateur, Kolonell
Passionate about digital and entrepreneurship in Africa, Mohamed has been helping Sénégalese businesses with their digital transformation since 2020. Founder of Kolonell, he believes every SME deserves a professional and accessible online présence.
