Free tool
How much will it cost to rewrite your old system?
The company still runs on Delphi, Access, Visual Basic or PHP from 2009, and the one person who knows it is close to retirement. Type in roughly how many lines of code it has and the language: get hours, cost and duration for a rewrite as a modern web app.
| Who rewrites it | Hours | Cost range | Duration |
|---|---|---|---|
| US product agency (Atomic Object, per Clutch) | … | … | … |
| Polish software house (Clutch, 2026) | … | … | … |
| European outsourcing, senior (Accelerance, 2026) | … | … | … |
| Me: senior engineer working with coding agents | … | … | … |
How the estimate works
- Lines of code become function points using the median lines per function point for the language from the QSM table (version 5.0, 2,192 projects). Delphi, PHP and Access are not in it, so “another language” assumes 50, the middle of the table.
- Function points become hours using the spread of hours per function point in the China dataset (PROMISE, n=499): the range shows the 25th to 75th percentile, the point estimate the median.
- The hours are priced at the same rates as the main estimator. My row is divided by the AI multiplier, because I rewrite with coding agents; market rows are not.
- A rewrite has an advantage the dataset does not: the old system is a working specification. It also has a cost the dataset does not: data migration and running both systems for a while. The two roughly cancel out; treat the range as a range.
Hours per function point in the data: p25 4.3, median 8.1, p75 15.4 (n=499). Currency at the NBP rate of 2026-10-16 (1 USD = 3.8827 PLN).
How a rewrite should go
- Start with the module people use most, rebuild it next to the old one and switch only that module.
- Migrate the data for each module when it switches, not all at once at the end.
- Keep the old system read-only until the last module moves, so nothing is lost.
- Write down how the new system runs from day one, so it never becomes the next legacy.
Questions
How much does it cost to rewrite a Delphi application?
It depends on its size. Enter the approximate number of lines of code: 50,000 lines is about 1,000 function points, which real projects delivered in roughly 4,300 to 15,400 hours at market pace.
Is it cheaper to rewrite with AI?
With coding agents, I need fewer hours than the market rows show, and the multiplier lets you set how many fewer. Agents are good at reading old code and rewriting it module by module; the decisions and the data migration still take people.
Do we have to stop using the old system?
No. A staged rewrite runs next to the old system and switches one module at a time.
Do you need to see our old code first?
For this estimate, no: it only uses the numbers you type. For a real quote I look at the code on the call.
Sources
- QSM, Function Point Languages Table, version 5.0 (median lines of code per function point)
- Zenodo / PROMISE (SEACRAFT): China effort dataset, CC BY 4.0 (hours per adjusted function point, PDR_AFP)
- Clutch, Software Development Pricing Guide 2026 (Poland $50–99/h)
- Accelerance, 2026 outsourcing rate trends (Europe senior $64–76/h)
- Clutch, Atomic Object profile (US agency $150–199/h)
- NBP, exchange rates table A
Want to rewrite it in stages, without stopping the company?
Bring the line count and the language to a free 30-minute call. I will propose which module goes first and what the first stage costs.
