Your London brand's stock lives in two countries now, and Cin7 still thinks it's one warehouse
Custom inventory software in London typically runs £40k to £130k over 3 to 7 months. You build custom when your stock reality outgrew the tool: split across a UK 3PL and an EU warehouse since Brexit, sold across multiple channels, with customs and duty logic no off-the-shelf system models. For a London brand, the trigger is the day you oversell because two systems disagreed on what was actually available.
Cin7 or Fishbowl handled your inventory fine when it sat in one London warehouse and sold through one channel. Then Brexit pushed you to hold EU stock in a continental warehouse to keep delivery times and avoid customs friction for European customers, and now you're running stock in two countries, two tax regimes, and several sales channels. The off-the-shelf tool sees a single pool of inventory and can't reason about which stock can legally and economically fulfil which order.
So you oversell, because the Shopify store, the wholesale channel, and the marketplace each pull from a view that doesn't reflect the real split. Customs and duty calculations for inter-warehouse transfers happen in a spreadsheet. Your ops team manually reconciles what the system says against what the 3PLs report. The inventory tool that was supposed to prevent stockouts and overselling is now the thing creating them.
Budgeting a inventory management build in London
| Project scope | Typical cost | Timeline |
|---|---|---|
| Custom multi-warehouse inventory engine | £60k to £110k | 4 to 6 months |
| Full inventory platform with customs and channel sync | £90k to £130k | 5 to 7 months |
| Order-routing and available-to-sell module only | £40k to £70k | 3 to 4 months |
The case for owning your inventory management
A London brand holding stock across UK and EU warehouses to manage post-Brexit fulfilment has an inventory problem off-the-shelf tools weren't built for: multi-country, multi-channel, with customs logic baked in. Custom inventory software models the real split, decides which warehouse fulfils each order on cost and legality, calculates duty on transfers, and gives every sales channel an accurate available-to-sell number. Overselling stops because the system finally reflects where your stock actually is and what it can do.
- You hold stock in both UK and EU warehouses and a single tool can't reason about the split
- Overselling happens because channels see inventory that isn't truly available
- Customs and duty on transfers is managed in spreadsheets
- You run multiple sales channels that need accurate, reconciled stock numbers
- You operate from one UK warehouse with a single sales channel
- Post-Brexit EU fulfilment isn't part of your model
- Cin7 or Fishbowl reconciles cleanly without spreadsheet workarounds
- Your SKU count and order volume don't justify a bespoke multi-warehouse engine
What your build should include
What we build under inventory management in London
The engagements London teams bring us most often: inventory tracking, Fishbowl alternative, Cin7 alternative, real-time inventory, purchase order management and demand forecasting.
Delivery, week by week
Exactly what you get
Inventory software that models where your stock actually is: split across a UK 3PL and an EU warehouse, sold across Shopify, wholesale, and marketplaces. The system decides which warehouse fulfils each order on cost, speed, and customs legality, calculates duty on transfers, and gives every channel an accurate available-to-sell number. Overselling stops because the picture is finally true, and your ops team stops reconciling 3PL reports against a system that disagreed with reality.
How to choose a developer in London
Choose a team that has built multi-warehouse, cross-border inventory before, because the customs logic and order routing are where these projects live or die. Ask how they'd decide which warehouse fulfils a Berlin order versus a Birmingham one, and how they'd cost an inter-warehouse transfer's duty. A partner who models inventory as a single pool hasn't understood your post-Brexit reality. Tie the build to your warehouse management system, supply chain software, and Shopify or commerce platform so stock, fulfilment, and sales stay aligned.
- Accurate available-to-sell per channel because the system models the real UK/EU split
- Order routing that picks the warehouse on cost, speed, and customs legality
- Duty and customs on inter-warehouse transfers calculated automatically, not in spreadsheets
- Overselling stops as every channel pulls from one true inventory picture
- Real-time reconciliation against 3PL reports instead of manual matching
- Multi-warehouse, multi-tax logic is genuinely complex and drives cost and timeline
- You own the customs and duty rules as they change, rather than the vendor maintaining them
- Integration with multiple 3PLs and channels is where most of the project risk lives
- If you operate from a single UK warehouse and one channel, off-the-shelf is the right call
- !They model inventory as one pool; ask how they handle the UK/EU split and order routing
- !No customs or duty logic; ask how inter-warehouse transfers get costed
- !They've integrated one 3PL ever; ask about syncing multiple feeds reliably
- !Available-to-sell is hand-waved; ask how they prevent overselling across channels
- !Quote without seeing your warehouse and channel map; ask for a stock-flow audit
If inventory management is on the roadmap, accounting, project management, lms usually follow within the year. Budget them as one conversation.
Rohan advises mid-market and enterprise teams on ERP, CRM and custom software, and has led delivery on dozens of business-software builds.
Writes for Digital Heroes, shipping business software for 2,000+ brands across 55+ countries since 2017.
Frequently asked questions
Why does Cin7 cause overselling for us now?
Because tools like Cin7 model inventory as one pool, while your stock is split across UK and EU warehouses with different fulfilment economics and customs rules. Channels pull from a view that doesn't reflect what's truly available where, so they oversell. Custom software models the real split.
How does order routing actually work?
The system evaluates each order against your warehouses and picks the one that fulfils it best on cost, delivery speed, and customs legality, sending a Paris order to the EU warehouse and a London order to the UK 3PL automatically rather than relying on a manual call.
Can it handle customs and duty on transfers?
Yes, and that's a core reason London brands build custom post-Brexit. The system calculates duty and customs on inter-warehouse transfers and cross-border orders, replacing the spreadsheet your ops team currently maintains by hand.
Will it sync with our Shopify and marketplaces?
Yes. The custom build pushes an accurate available-to-sell number to every channel from one true inventory picture, which is exactly what stops the overselling that channel-by-channel views cause.