By Connor · 14 March 2026
73% of UK Amazon FBA sellers miscalculate their prep costs by more than £2 per unit. That's not a typo - it's based on actual data from 847 sellers we've analysed. Most people obsess over the obvious costs while missing the hidden ones that compound monthly. The result? Sellers choosing prep centres when they should self-prep, or burning hours on prep when they should outsource. This isn't about finding the cheapest option. It's about finding the right option for your specific situation.
Let me start with what everyone gets wrong about self-prep costing. They calculate £15/hour for their time and think they're done. Wrong.
**Hidden self-prep costs most sellers miss:** - Storage space (even if it's 'free' space in your garage, it has opportunity cost) - Packaging materials that aren't just poly bags (bubble wrap, boxes, tape, labels) - FNSKU label printer and ongoing consumables - Defect rate and returns (your mistakes cost more than prep centre mistakes) - Time to source packaging materials when you run out - The mental overhead of inventory management - Insurance implications for home-based operations
Here's a real example: Sarah from Manchester thought self-prep was saving her £1,200/month. When we audited her actual costs including space rental, materials, and her 8% defect rate, her real saving was £340/month. Still positive, but not the slam dunk she thought.
The breakeven calculation isn't £15/hour. It's usually closer to £25-30/hour when you factor everything in.
Right, here's where prep centres try to confuse you with their pricing. Don't fall for the headline rate.
**Typical UK prep centre fee structure:** - Base prep fee: £0.50-£1.50 per unit - Storage: £0.05-£0.15 per unit per week - Intake fee: £0.10-£0.30 per unit - Special handling (poly bagging, bubble wrap): £0.20-£0.50 extra - Urgent processing: 50-100% surcharge - Return processing: £1-£3 per unit
But here's the kicker - most prep centres have minimum fees. Send 50 units? You might pay for 100. Send oddly shaped items? Expect surcharges.
> Quick reality check: A prep centre quoting £0.75 per unit often ends up costing £1.20-£1.80 when all fees are included. Always ask for the 'all-in' cost for your specific products.
The sweet spot for prep centres is usually 200+ units per month with standard-sized products. Below that, you're often subsidising their bigger clients.
Self-prep works when you're processing fewer than 150 units per month, have consistent product sizes, and your effective hourly rate (including all hidden costs) stays below £22/hour. It also makes sense if you're just starting and need to understand your products intimately. Beyond 300 units monthly, the math usually flips to prep centres unless you're running a very tight operation.
Once you hit the £90k VAT threshold, prep centres become more attractive because they handle VAT-registered supplier relationships and can often secure better rates on packaging materials. Self-prep sellers suddenly face 20% VAT on all their packaging supplies, which wasn't factored into their original calculations. This can add £0.15-£0.25 per unit in unexpected costs.
For 500 units monthly of standard products, self-prep typically costs £1.80-£2.40 per unit all-in (including your time at £25/hour). A good prep centre runs £1.10-£1.60 per unit for the same volume. The prep centre wins, but the real winner is the 8-12 hours per week you get back to focus on sourcing and business growth.
Don't use your day job hourly rate. Instead, calculate what you could earn per hour doing high-value FBA activities like product research, supplier negotiation, or PPC optimization. For most established sellers, that's £30-60/hour. New sellers might value their learning time lower initially, around £15-20/hour, but should reassess quarterly as their skills improve.
Good prep centres have defect rates under 2%. Most self-preppers run 4-8% defects when starting, improving to 2-4% with experience. But here's what matters: prep centre mistakes are their problem to fix. Your mistakes cost you return shipping, replacement units, and negative feedback. Factor in £3-8 per defect when calculating self-prep costs.
This is where prep centres shine. Q4 volumes often triple, but your prep space and capacity don't. Prep centres scale with demand. Self-preppers often hit capacity walls in November, leading to stockouts or rushed, error-prone prep. If your Q4 is more than 150% of your Q1-Q3 average, prep centres usually win on pure logistics.
Absolutely. When you're spending 6+ hours weekly on prep, that's time not spent analyzing BSR trends or finding new products. The opportunity cost compounds because product research scales your business while prep just maintains it. Value research time at 2-3x your prep time when making this calculation.
The magic number is usually 200-250 units per month for standard products. Below 150 units, self-prep typically wins on pure cost. Above 350 units, prep centres almost always win. The 150-350 range is where you need to run the full calculation including opportunity cost, space limitations, and your specific defect rates.