This page explains, in plain language, how every calculator on ToolJagat is built, tested and kept accurate.
1. One formula, one tested function
Each calculation lives in a single small program function that has no connection to the screen. For example, the EMI formula is one function; the SIP formula is another. The on-screen tool only collects your inputs and displays what the function returns. This means the number you see is exactly the number the formula produces, with no copy-paste layer in between.
2. Automated tests with verified answers
Every function has at least five automated test cases. The expected answers in those tests were worked out independently (by hand or with a second method) and confirmed by the site owner before the tool was published. Examples of answers our tests lock in:
- Loan of ₹10,00,000 at 10% per year for 20 years → EMI ₹9,650.22
- SIP of ₹5,000 per month at 12% per year for 10 years → maturity value ₹11,61,695
- ₹12,50,000 → "Rupees Twelve Lakh Fifty Thousand Only"
If any test fails, the website cannot be deployed until it is fixed.
3. Standard formulas
- EMI: reducing-balance formula EMI = P × r × (1+r)ⁿ ÷ ((1+r)ⁿ − 1), where r is the monthly rate (annual ÷ 12 ÷ 100) and n the number of months. This is the method used by Indian banks and NBFCs.
- SIP: future value of an annuity due, FV = P × ((1+i)ⁿ − 1) ÷ i × (1+i), with investment at the start of each month, matching AMFI and fund-house calculators.
- Age: calendar arithmetic in whole years, then months, then days, with leap years and month lengths handled correctly.
- Number to words: the Indian numbering system (hundred, thousand, lakh, crore, arab) in English and Hindi, with rupees and paise.
- Percentage: standard arithmetic, rounded to two decimal places to avoid floating-point artefacts.
Each tool page repeats its formula with a worked example that is computed by the same function at build time.
4. Rates and rules come from official sources only
Where a tool depends on a government rate or rule (for example tax slabs or stamp duty), the figures are stored in a data file that records the official source URL, its title, the date we verified it and the date it came into effect. These figures are never written from memory. If an official source is not available, the tool is not published.
5. Rounding and formatting
Money is rounded to two decimal places (paise) for EMIs and to the nearest rupee for long-term projections, which is how banks and fund houses present them. Amounts are displayed in the Indian format (₹12,50,000). Small differences from a bank's own figure can arise from its rounding, day-count convention or fees.
6. Your data stays with you
All tools run in your browser. Inputs are not transmitted to or stored on our servers. See the Privacy Policy.
7. Verification dates and updates
Every tool page shows a "Last verified" date. We re-check tools when rules change, when a user reports an issue and on a periodic schedule. Corrections are noted on the page.