Most agency owners run this decision on salary versus day rate, and reach the wrong answer. A £55,000 Shopify developer looks obviously cheaper than £400 a day until you price the two things the salary comparison leaves out: utilisation and idle risk.
The real cost of a hire
A £55,000 salary is roughly £70,000 fully loaded once you add employer NI, pension, equipment, software, recruitment amortised over expected tenure and holiday cover. Across 220 working days that is about £320 a day — before you account for the fact that no developer is billable every day.
At 70% utilisation, which is healthy for an in-house developer who also does internal work and support, the true cost per billable day is around £455. At 50% — common in agencies where Shopify work arrives in bursts — it is £640.
The break-even, honestly stated
Outsourcing at £400 a day beats an in-house hire until you can reliably fill more than roughly 12–14 days of Shopify work a month, every month, for at least a year. Below that line you are paying for idle capacity. Above it, the hire wins on cost and on the compounding value of someone who knows your clients.
The word doing the work in that sentence is "reliably". Two good quarters is not a trend. If your Shopify pipeline depends on one client's roadmap, you are one relationship away from carrying a salary with nothing to put against it.
Cost is not the only axis
Hiring wins on context. An in-house developer learns your clients, your design system and your deployment conventions. By month six they are answering questions that would otherwise become tickets. That value never shows up in a day rate comparison but it is real.
Outsourcing wins on elasticity and on peak specialism. You can take a Plus migration or a checkout extension project without hiring for a skill you will use twice a year, and you can say yes to a deadline that your current team cannot absorb.
The hybrid that most agencies land on
The stable pattern we see: one in-house developer who owns client relationships, everyday changes and quality control, plus an outsourced partner on a small monthly commitment for overflow and specialist work. The in-house engineer reviews what comes in, which keeps standards yours rather than the supplier's.
This also solves the bus-factor problem. If your single Shopify developer resigns, an established partner already knows your stack and conventions, and you have weeks rather than days to react.
Before you decide, measure one number
Count the Shopify development days you actually billed over the last twelve months, not the ones you quoted. If it is under 140, outsource. If it is over 200 and growing, hire. Between the two, hire one person and keep a partner on a five-day monthly commitment — the cheapest way to buy both context and elasticity.