TrueCalci documentation
How the calculators work, which laws they follow, and how to call them from your code or an AI agent.
1. Why a calculator instead of the model
Language models such as Claude, GPT and Gemini predict text. They are good at understanding a question and unreliable at long, exact arithmetic over tax brackets, amortization schedules and compound growth.
TrueCalci does the arithmetic. Tax and money figures use exact decimal arithmetic and dated rate tables; engineering and scientific formulas use standard double-precision floating point. The same inputs always return the same output.
Every statutory figure (rates, slabs, caps, limits) comes from a rule set with a start and end date and a source. The figures are not repeated on this page so they cannot go out of date here; a calculation returns the values it used. Past a rule set’s end date a tool refuses to answer instead of guessing. The compliance page lists sources and review cadence.
2. Laws and sources
The tax and finance calculators follow published law and regulator guidance:
Compares a W-2 salary with a 1099 contract rate: self-employment tax (Social Security up to the year’s wage base, plus Medicare), the employer share an employee does not pay, benefits and unpaid time, and the qualified business income deduction.
break-even hourly rate = (salary + employer taxes + benefits + paid time off) / billable hours
Shareholder-employees must take a reasonable salary before distributions. The calculator compares payroll taxes on the salary and distribution split you enter; it does not decide what is reasonable for you.
Employee deferral (with catch-up by age) plus employer profit sharing, capped by the year’s total annual addition limit. The limits change every year and are read from the rule set for the year you ask about.
Slabs, standard deduction, the rebate and its marginal relief, surcharge and the health and education cess for the tax year you choose, under the new or the old regime.
Monthly principal, interest, property tax and insurance (PITI), and when private mortgage insurance ends: automatically at 78% of the original value, or on request at 80%.
Adds VAT to a net amount or extracts it from a gross one, at each member state’s rates, and flags the reverse charge for cross-border business-to-business services.
3. Model Context Protocol (MCP) Integration
TrueCalci is a remote Model Context Protocol (MCP) server. Claude and other MCP clients connect to it over Streamable HTTP at https://truecalci.com/mcp. Every tool only calculates: none of them changes data, sends anything or spends money, so each is marked read-only.
Use TrueCalci in Claude
claude.ai and Claude Desktop (any plan that allows custom connectors):
- Open Customize → Connectors and choose Add custom connector.
- Name:
TrueCalci. URL:https://truecalci.com/mcp. Select Add. - In a chat, open the tools menu and make sure TrueCalci is switched on.
Claude Code:
claude mcp add --transport http truecalci https://truecalci.com/mcp
claude mcp login truecalci
Sign-in. Claude can list the tools and read the rate tables without an account. Calculations need sign-in: in Claude Code run claude mcp login truecalci (or /mcp, then choose truecalci); in Claude on the web or desktop, Claude opens our authorization page (OAuth 2.0) when you connect. If you are not signed in, enter your email on that page and type the 6-digit code we send (a free account is created the first time), then select Allow. Calls then count against your plan’s allowance. You can remove Claude’s access at any time from your account page under Connected apps. What a connection stores is described in the Privacy Policy.
Example prompts
- “Using TrueCalci, compare my Indian income tax under the new and old regimes on a salary of ₹18,00,000.”
- “What is the monthly EMI on a ₹50,00,000 home loan at 8.5% for 20 years, and how much interest will I pay in total?”
- “Work out GST on a ₹1,00,000 inter-state supply at 18%.”
- “I earn $95,000 as a W-2 employee. What hourly rate would I need as a 1099 contractor to take home the same?”
- “Find the NPV and IRR of a project costing $100,000 that returns $30,000 a year for five years at a 10% discount rate.”
Tax and rate calculators return the rates and sources they used. If an input is missing or out of range, the tool says which one and why, so Claude can ask you.
Other MCP clients
Cursor (.cursor/mcp.json) and most other clients take the same URL:
{
"mcpServers": {
"truecalci": { "url": "https://truecalci.com/mcp" }
}
}TrueCalci is also listed on Smithery and Glama. Help: Support or support@truecalci.com.
Some of the tools
npv_irr
Capital budgeting: Net Present Value, Newton-Raphson IRR, and payback timelines.
cagr_inflation
Nominal CAGR, real purchasing power retention (Fisher equation), and exact doubling horizons.
breakeven_margin
Unit and revenue break-even thresholds, contribution margin ratio, and margin of safety.
contractor_parity
1099 vs W-2 breakeven hourly rate, SECA arbitrage, and QBI tax drag.
mortgage_piti
Monthly mortgage PITI, CFPB Reg Z escrow, and automated PMI termination.
black_scholes
Analytical option Greeks (Delta, Gamma, Vega, Theta, Rho) with normal CDF.
beam_bending
Euler-Bernoulli beam deflection, shear moment diagram, and elastic section modulus.
ai_token_arbitrage
Prompt cache arbitrage, KV cache retention, and GPU cloud interconnect FinOps.
4. REST API
Try the REST API here. Pick a calculator, edit the JSON input and run it. Calls need an API key: sign in (free) and create one on the Developer page.
{
"status": "ready",
"message": "Press Run to call the API."
}
Every error code returned in error_code is documented, with the HTTP status, what it means and how to fix it, at
GET /api/v1/errors. Stuck on something the catalogue doesn't answer? Send it to
support@truecalci.com or POST /api/v1/support.
A working example input for every MCP tool is at
/docs/mcp-examples.json.
5. Official sources
The government and standards bodies whose published rules the calculators follow: