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We Moved Desktop Accounting Software to the Web: TurboCASH 4, Rules and Books Included

We converted the core of TurboCASH 4, open-source Windows accounting software written in Delphi on a Firebird database, into a web app on React, C# and PostgreSQL. We read its UK starter books out of the old database, wrote its posting rules down from the source, and ran its arithmetic, which showed that at 20% VAT one VAT-inclusive amount in six splits a penny over. The web version keeps the rules and rounds VAT once. It’s an independent conversion of the GPL version, and you can try it with a fictional company.

Last updated 3 min read

A lot of small businesses keep their books in a Windows program installed years ago. It works, so nobody touches it. Then the PC needs replacing, the bookkeeper wants to work from home, or the accountant asks for access, and the program can’t go along.

After our first conversion, a small invoicing program, we wanted something stricter: real double-entry accounting, where every posting has to balance and a penny matters. TurboCASH 4 fits. It’s open-source accounting software for Windows, written in Delphi on a Firebird database and released under the GPL, so every step can be shown.

Try the web version → It opens on Fernley Joinery Ltd, a made-up UK joinery workshop with last year and this year posted. Your copy is yours alone.

This is an independent conversion of the GPL version 4. It isn’t made or endorsed by TurboCASH’s publishers, who still sell a later version.

What we did

  1. Got the books out. TurboCASH 4’s UK starter books are a Firebird 1.5 database, a format today’s Firebird won’t open. The installer brings its own older Firebird, and that one reads them: 74 accounts, four VAT rates and eleven journal types, read once into the web version.
  2. Wrote the posting rules down. Nearly all of them are in one source file. Nothing posts to a control account or to an account with sub-accounts. A date must fall in an open period of this year or last year. A batch must balance in every period before anything is written. In a cash book the VAT goes with the expense and the bank takes the whole amount.
  3. Ran the old arithmetic. For a VAT-inclusive journal line, TurboCASH 4 rounds the net and the VAT separately. Run on every amount from £0.01 to £1,000.00, one in six comes out a penny over at 20%: £12.15 becomes £10.13 plus £2.03. Its balance check allows no difference. We found this in the code and proved it with the arithmetic; we didn’t watch the program refuse a batch.
  4. Decided what to fix. VAT is now rounded once, so the net and the VAT always add up to what was typed. A customer going over their credit limit gets a warning (the original only warned for suppliers). Dates before the books are refused. A VAT account the starter books pointed at but didn’t contain is repaired on import.
  5. Built it on a standard stack: React screens, a C# API and PostgreSQL. It keeps what TurboCASH users know: the account codes, the journal names, Update ledger as its own step, F5 to balance and F6 to post, and separate rights for entering and posting.

The conversion took about 50 minutes, with an AI coding assistant doing the work and a person choosing the program and the scope.

What it can do

  • The chart of accounts, with balances and each account’s entries
  • Debtors and creditors: terms, credit limits, age analysis, open items, payments allocated to invoices, statements
  • Stock items with average cost
  • Invoices, credit notes, quotes, orders, purchases and supplier returns, with the ledger entries shown before they post
  • Batch entry in the original’s journals, posted batches and reversals
  • Trial balance, income statement, balance sheet, age analysis and a VAT report
  • A clerk who enters work and an owner who posts it

It’s the core of TurboCASH, not all of it: no point of sale, multi-currency, budgets, bank import or report designer.

Why it matters if your books are in an old program

Accounting software is where a conversion has to be most careful. The rules about what may post, and where, are what your bookkeeper and accountant rely on, and a changed total is never small, even by a penny. That’s why we read the rules first, run the old arithmetic, and list every difference for you to decide.

The case study has every step: the books, the rules, the arithmetic, what we fixed and what we kept, and the timings. If your business still keeps its books or invoices in an old desktop program, tell us about it. The first call is free.

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