Legacy core banking systems quietly swallow most of a bank’s technology budget, and the bill grows every year. So we asked banking and technology leaders a direct question: what does staying on old infrastructure truly cost, and when does modernisation finally pay for itself? These are people who have lived through migrations, budgets, and the odd disaster. Their answers point to a clear pattern. The real damage rarely shows up on the server invoice. Instead, it hides in slow decisions, lost trust, and missed revenue.
What Legacy Core Banking Really Costs
Maintenance on a legacy core banking estate looks like a fixed cost, yet it behaves like a tax that climbs each year. Accenture reports that banks spend close to 70% of their technology budgets just keeping current systems running. McKinsey frames the same problem differently, noting that banks turn only five to ten cents of every tech dollar into real business value. So banks keep very little for new products or better experiences.
The hidden costs bite harder. Specialist talent grows scarce as veteran engineers retire, and the few who still read decades-old code command premium rates. The risk is human as much as technical. When only a handful of people understand the oldest code, a single retirement can stall a release for weeks. Meanwhile, every small change can drag on for months, so the bank steadily loses ground to faster rivals. For owners watching their own overheads, the lesson rhymes with our guide on cutting business expenses.
The drain is global, not local. IDC expects worldwide spending on outdated banking technology to climb from roughly $36 billion in 2022 to about $57 billion by 2028. Every dollar locked into a legacy core banking platform is a dollar that cannot fund instant payments, smarter fraud defence, or the AI features customers now expect.
The real cost of legacy core banking isn’t the server bill. It’s the compound interest on every slow product decision. When a simple customer-facing change takes months because the core can’t expose data cleanly, the bank pays in missed revenue, higher support load, security workarounds, and talent frustration.
- Roman Surikov, Founder, Ronas IT | Software Development Company
That compounding effect explains why the maintenance figure keeps climbing rather than shrinking. Several leaders we spoke with put hard numbers on the drain.
Legacy core banking systems carry high maintenance costs and demand specialised skills that keep dwindling. Those costs can reach 70% of a bank’s IT budget. Modernisation frees that money for stronger customer engagement and growth.
- Michael Kazula, Director of Marketing, Olavivo
When Modernisation Finally Pays Off
Timing is the question every board asks, and the evidence offers a workable answer. Most core programmes reach positive return within three to four years, according to industry analysis built on McKinsey data. Better still, the early wins arrive sooner. EY and FIS report efficiency gains of 20% to 35%, a 15% to 30% drop in cost per account, and product launches that run 30% to 90% faster.
Modernisation reverses the maths that legacy core banking imposes on every team. When the core exposes clean data through open interfaces, staff ship features in weeks instead of quarters. Banks that escape legacy core banking early also free their best engineers from constant firefighting. As a result, the payoff stops being a vague promise about fresh architecture. It turns into a measurable change in cost, speed, and risk. These gains track the wider fintech trends reshaping the sector.
The trick is to tie the business case to numbers the board already tracks. Cycle time, incident counts, integration spend, and launch speed all move in the right direction once the core stops fighting back. When the case rests on those metrics rather than on buzzwords, approval gets far easier.
For one contributor, the clearest signal of payoff sits with the customer, not the server room.
The hidden cost of legacy systems is almost always trust, not tech. Modernisation pays off the moment your frontline can give a confident answer faster than yesterday. That’s the metric I’d track, not just server costs, but speed-to-confident-answer for the customer sitting across the desk.
- Ydette Macaraeg, Marketing Coordinator, Santa Cruz Properties
The Risk of Getting It Wrong
Modernisation still carries its own danger, and the cautionary tales run expensive. When TSB attempted a single large migration in 2018, the new platform failed on launch. The bank locked millions of customers out of their accounts and lost around 80,000 of them. All told, it spent roughly £330 million before regulators added a £48.65 million fine. IBM research underlines how common the trouble is, since 94% of surveyed banks sit behind schedule on core modernisation.
These failures do not argue for keeping legacy core banking in place, though. The lesson is not to avoid change, but to sequence it. Rather than replacing everything at once, the safer route carves out one domain, proves the value, then expands. Regulators reinforce that caution too, because an active core transformation now draws far closer supervisory attention.
Legacy core banking systems tie up as much as 80% of IT budgets through manual processes, so they leave little for innovation. They also struggle to keep pace with new regulations, which raises compliance risk and the chance of fines.
- Mohammed Kamal, Business Development Manager, Olavivo
Where Smart Banks Start
The leaders agree on a practical first move. They map the true cost of their legacy core banking estate, then pick the single module that blocks revenue or trust most directly. From there, they modernise in stages and measure each step against one clear metric.
Commonwealth Bank of Australia shows the model working at scale. The bank moved its core to the cloud in roughly 18 months. It now runs close to half the nation’s payments on the new platform, with sharper performance. Smaller lenders prove the same point on tighter budgets. Judo Bank, an Australian SME lender, replaced its legacy core banking setup and cut product development time by half, often shipping a working pilot inside a single year.
So the answer to our original question is refreshingly concrete. Legacy core banking costs the most when its drag becomes measurable and recurring. Modernisation pays off the moment it removes a specific bottleneck that the business can feel. For most banks, the real choice is no longer whether to leave the old core, but how fast and how safely. Teams weighing the move can first study how others develop fintech infrastructure before they commit.
