Calculate your project price.
On your phone or computer.

Offline on your computer

2. Download it. Use it offline.

To calculate without internet access, download the package to your computer. The standalone calculator does not send your entered prices to a server. On an iPhone, use the web calculator; HTML files opened in the Files app may not run calculations.

Download ZIP for your computer

1. Extract the downloaded ZIP.

   The package contains kalkulacka.html, a short guide and the Codex prompt. On a Mac, double-click the ZIP; on Windows, choose “Extract All”.

2. Open kalkulacka.html in a browser.

   On a Mac, use Safari or Google Chrome. If double-clicking opens a text editor, right-click the file and choose Open With, then your browser. The address bar will show a local file. No account or AI is needed to use the calculator.

3. Load the sample, then change the inputs.

   Select “Load sample figures”. Costs should be €700, price €1,000 and the amount above costs €300. Then enter your own four values. The hourly cost rate is your internal cost, not the rate charged to the customer.

4. Save your calculation before closing.

   Select “Save calculation as JSON” and check the saved file. Next time, open the HTML and select “Load JSON”. Saving and loading works the same way as in the web version.

Optional · build your own

3. Build your own with Codex.

You can use the finished calculator above straight away. This section is for trying to build your own app. You need a desktop app with Codex, a login, internet access and an empty folder. Check availability and limits in the current OpenAI overview.

1. Prepare an empty folder and open Codex.

   Create a folder named moja-kalkulacka. Open your desktop app and select Codex. If you do not have the app yet, start with the official OpenAI instructions and sign in with your own account.

   Start a new chat for this folder. Choose local work on your computer, labelled Local or This computer; when choosing a project or folder, open moja-kalkulacka. GitHub and a cloud environment are not needed. Controls may move between versions; see projects and chats and the local Codex environment.

2. Copy the full prompt and send it in the chat.

   Use the button below, paste the text into a new chat and send it. If Codex requests folder access or permission to write a file, check that it is working in moja-kalkulacka. You can also download the prompt as TXT.

   Copy full prompt

   Create a simple offline project-price calculator as a single kalkulacka.html file with embedded CSS and JavaScript. It must open by double-clicking in a browser using file://, without a server, account, API, CDN, external fonts, analytics or network requests. Using it must not require AI. Do not create a framework or extra features.
   
   Use an English interface, EUR and amounts excluding VAT. Use a readable light layout, system fonts, visible focus and keyboard controls. Inputs: material and other direct costs, hours of labour, internal hourly cost rate and target margin percentage. Explain that cost rate is not the selling rate and margin is not markup.
   
   Costs N = material + hours × cost rate. Recommended selling price P = N / (1 − margin / 100). Amount above entered costs R = P − N. Never call R net profit. Overheads, taxes and other costs not entered are not included.
   
   Include buttons to load made-up sample figures, clear inputs, export the calculation as JSON and import JSON. The JSON format must have its own identifier and version. Invalid imports and unsupported versions must leave existing inputs unchanged. Check structure, data types and file size. Never render imported data using innerHTML or use eval. Do not save calculations automatically. Clearly tell users to export before closing; do not rely on localStorage.
   
   Accept decimal commas and points. Money permits at most 2 decimal places, hours and percentages 4. Material: 0 to €1 billion; hours: 0 to 1 million; rate: 0 to €1 million/hour. Margin: 0 to less than 100%. Maximum result: €1 trillion. Reject blank inputs, negative numbers, non-numeric and excessive values with clear errors. Clear outdated results on error and restore them when corrected.
   
   Calculate accurately in cents. Round labour cost to cents first, add material, then round selling price to cents. Round an exact half-cent up. Derive R from the displayed figures. Explain that rounding may slightly change the achieved margin. With zero costs, price is €0; a percentage margin at a zero price is undefined. Keep calculation functions separately testable. No discount, VAT, currency selection or other additions.
   
   Test the resulting HTML, not just an isolated formula. Check: material €400, 10 hours × €30, margin 30% gives costs €700, price €1,000 and amount above costs €300. Also test zero margin, zero costs, decimal values, invalid inputs and correction, export → close → reopen → import, malformed JSON and an unsupported version. Check operation without network access in a separate browser context; do not disconnect the whole computer. State the browser actually tested and any unverified parts. Finally show the file and brief instructions for opening it and saving calculations.
   

3. Find the generated file and open it in your browser.

   When finished, open the moja-kalkulacka folder and its kalkulacka.html file. Load the sample. With material costs of €400, labour of 10 × €30 and a 30% margin, the price should be €1,000. Then check saving and reloading the calculation. Your version may look different; the check figures should match.

   

4. If something is wrong, continue in the same chat.

   For example: “With material costs of 400, labour of 10 × 30 and a 30% margin, I expect a price of €1,000. The app shows something else. Find the cause, fix it and repeat the check.” Use made-up figures. Do not send JSON containing real business prices to Codex.