Free calculators that respect your privacy
ModernCalcs is a collection of 500+ free online calculators and converters for finance, health, developer tools, and everyday needs. Every tool runs entirely in your browser — your inputs never leave your device.
What we stand for
Privacy by design
Every calculation runs entirely in your browser using JavaScript and the Web APIs your device already has. No data is sent to any server, no accounts, no cookies that track you across sites. A calculation you do on ModernCalcs stays on your device.
Accuracy first
Each tool is built from verified formulas — tax slabs from official ITD notifications, financial formulas from actuarial standards, health metrics from WHO and peer-reviewed sources, and developer tools from official RFCs and language specifications. Where a formula has known limitations, we document them.
Client-side only
With very few exceptions (tools that require a language runtime like curlconverter), all computation is done in the browser. This means the tool works offline once loaded, is not subject to server downtime, and cannot leak your inputs in transit.
No dark patterns
No paywalls, no registration walls, no 'try 3 calculations free then subscribe'. Every tool on this site is free and fully functional. No ads that track you. No affiliate links without disclosure. No fake urgency.
What's on ModernCalcs
The site covers six major categories with tools ranging from simple unit converters to multi-step financial planners.
| Category | Tools |
|---|---|
| Finance | 90+ |
| Health | 60+ |
| Developer | 240+ |
| Utilities | 50+ |
| Math | 40+ |
| Content & AI | 30+ |
How we ensure accuracy
- Tax slab rates and thresholds are sourced from official CBDT/ITD Budget notifications, updated each financial year.
- Financial formulas (compound interest, EMI, SIP) are derived from actuarial standards and cross-checked against known outputs.
- Health metrics (BMI, BMR, TDEE) use established clinical formulas with methodology notes on each tool page.
- Developer tools follow official RFCs, language specifications, and documented encoding standards.
- Each tool page documents the formula used and its source, so you can verify the calculation independently.
- When a tool covers a domain with professional licensing requirements (legal, medical, financial advice), the tool includes a disclaimer that it is informational and not a substitute for professional advice.
Privacy — the short version
ModernCalcs does not collect, store, or transmit your calculator inputs. Numbers you enter into a salary calculator, a BMI checker, or a password strength tool are processed locally by your browser and discarded when you close the tab.
The site uses Vercel Analytics (page view counts, no personal data) and Vercel Speed Insights (performance metrics, no personal data) for operational visibility. No third-party ad networks, no cross-site tracking pixels.
Tools that call external APIs (certain AI writing tools that use the Groq API) disclose this on their page. The API call is made directly from your browser to the third-party service — ModernCalcs does not proxy or log these requests.
Feedback & corrections
Found a calculation error? A tool that doesn't work in your browser? A missing tool you'd find useful? We want to know.
For formula corrections — especially tax or financial tools — please link to the official source (ITD notification, RBI circular, etc.) so the fix can be verified before publishing.