The verdict in three sentences
A PHP 5 application with no security patch since 2018 is an operational risk, not just technical debt. In Dublin in 2026, an incremental rewrite (strangler pattern) to Next.js with a typed API costs roughly 70,000 to 140,000 EUR over 4 to 6 months, plus 8,000 to 15,000 EUR for data migration. A big bang rewrite looks cheaper on paper, but it overruns by 30 % on average and freezes the business during cutover.
Why a PHP 5 application becomes a board-level problem
PHP 5.6 has not received a security fix since late 2018. In a 150-employee company, the internal application (quotes, scheduling, production tracking, inventory) often holds ten years of business rules written without automated tests. The symptoms are familiar: one developer knows how to change it, the host charges for an off-catalogue dedicated server, every change takes three weeks instead of three days, and the cyber insurer's audit flags the version.
| Indicator | Typical PHP 5 application | After Next.js rewrite |
|---|---|---|
| Security patches | None since 2018 | Monthly updates |
| Average lead time for a change | 2 to 4 weeks | 3 to 8 days |
| Test coverage | 0 to 5 % | 60 to 80 % on core logic |
| Annual hosting | 4,000 to 8,000 EUR (dedicated server) | 1,500 to 4,000 EUR (managed cloud) |
| Screen load time | 3 to 8 s | 0.5 to 1.5 s |
| Key-person dependency | High (1 developer) | Low (documented code, standard stack) |
Strangler or big bang: what each approach costs in Dublin
The strangler pattern puts a router in front of the old application and replaces modules one at a time. Users switch screen by screen, and the old code stays read-only until the new module is signed off. A big bang rewrites everything in parallel and switches over one weekend.
| Item | Incremental rewrite (strangler) | Big bang rewrite |
|---|---|---|
| Code audit and business rule mapping | 7,000 to 12,000 EUR | 7,000 to 12,000 EUR |
| Next.js + API development | 52,000 to 105,000 EUR | 48,000 to 95,000 EUR |
| Data migration and cleansing | 8,000 to 15,000 EUR | 8,000 to 15,000 EUR |
| Testing and user acceptance | 6,000 to 12,000 EUR | 9,000 to 18,000 EUR |
| Duration | 4 to 6 months | 5 to 8 months |
| Average observed overrun | 5 to 10 % | 30 % |
| Business downtime | None | 2 to 5 days |
Dublin day rates in 2026 for a senior full-stack developer sit between 650 and 850 EUR. A 90 to 160 person-day project therefore lands within the range above. For comparison, the same scope delivered from Nantes runs 40,000 to 75,000 EUR excluding VAT.
The four risks to lock into the contract
- Undocumented business rules: reserve 10 % of the budget to extract logic hidden in SQL queries and stored procedures.
- Data quality: duplicates, Latin-1 encodings, zero dates. A migration sample should be delivered in month one.
- Change management: train departmental champions before each module cutover.
- Reversibility: source code, migration scripts and documentation must belong to you, in writing.
Mini case study
Sarah, CIO of a 150-employee manufacturer near Dublin, runs a PHP 5 production tracking application. Her single developer bills 25,000 EUR a year for maintenance, dedicated hosting costs 6,500 EUR and the team loses about 6 hours a week on Excel workarounds, 280 hours a year at 55 EUR loaded, or 15,400 EUR. Annual cost of doing nothing: 46,900 EUR. The incremental rewrite is quoted at 98,000 EUR plus 12,000 EUR for migration, 110,000 EUR in total. After cutover, maintenance and hosting drop to 14,000 EUR a year and the workarounds disappear. Annual saving: about 32,900 EUR, payback in 3.3 years, before counting the cyber risk avoided.
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FAQ
How long does a PHP to Next.js rewrite take for a mid-sized company?
Allow 4 to 6 months with an incremental approach for an application of 30 to 60 screens. The first module usually goes live after 6 to 8 weeks.
Can we keep the existing MySQL database?
Yes, during the transition it is actually recommended: the new code reads the same database. A move to PostgreSQL, if useful, happens at the end of the project for 5,000 to 10,000 EUR.
Why Next.js rather than upgrading to PHP 8?
A PHP 8 upgrade costs 25,000 to 50,000 EUR in Dublin but keeps the original architecture. Next.js with TypeScript brings strict typing, fast screens and a much wider developer pool in 2026.
What is the main cause of budget overrun?
Business rules discovered mid-project. A 5 to 10 day audit upfront reduces that risk and keeps overruns under 10 %.
Do we have to freeze new features during the rewrite?
Not with the strangler pattern: new requests are built directly on the new stack, so you never pay twice.
Let's scope your project. Send us your list of screens and data volumes, and we will price an incremental rewrite with an indicative budget and a module-by-module plan. Detailed quote within 48 h. 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.
