A modern, responsive single-page investment calculator that calculates compound interest with various compounding periods, additional investments, and detailed financial metrics. Built with pure HTML, CSS, and JavaScript - no external dependencies.

• Features
• Quick Start
• Responsive Design
• Calculation Details
• Internationalization
• Technology Stack
• Technical Implementation
• Customization
• Privacy & Security
• Disclaimer
• License

• Compound Interest Calculation: Accurate calculation with daily compounding precision
• Multiple Compounding Options: No compounding, daily, monthly, quarterly, semi-annually, and annually
• Additional Investments: Regular additional investments with flexible frequency
• Effective Annual Rate: Calculates true annualized return considering compounding effects
• Real-time Calculations: Instant updates on every parameter change

• Final Amount: Total investment value at the end of the term
• Total Profit: Absolute profit and percentage gain
• Effective Rate: Actual annualized return (CAGR)
• Theoretical Monthly Income: Potential monthly income from final amount
• Average Monthly/Annual Profit: Real average capital growth rates
• Inflation Adjustment: Input expected inflation to see the real (inflation-adjusted) growth of your investment, visualized on the chart.
• Key Milestones: Time to double, tenfold, and hundredfold investments
• Target Income Timeline: When monthly income reaches target level
• Monthly Income Plan: Detailed month-by-month growth breakdown

• Responsive Design: Works on desktop, tablet, and mobile devices
• Language Support: English and Russian localization
• Modern UI: Clean, minimalist design with neobrutalism aesthetics
• Interactive Growth Chart: A dynamic SVG chart visualizes investment growth over time, featuring:
  • Interactive tooltips with precise data on hover.
  • Dynamic axes and grid lines that adapt to the selected term.
  • Color-coded milestone markers directly on the chart.
• Real-time Updates: All calculations update instantly
• Comprehensive Tooltips: Detailed explanations for all parameters
• Header Controls:
  • Theme Toggle: Switch between light and dark modes for comfortable viewing. Your preference is saved for your next visit.
  • Reset Form: Instantly clear all inputs and return to the default values.
  • Share Scenario: Generate a unique URL with all current parameters to share your calculation with others.
  • Language Toggle: Switch between English and Russian.
• Persistent State: Your last entered values are automatically saved in your browser, so you can continue where you left off.

Simply open index.html in any modern web browser. No installation or build process required.

The calculator is fully responsive and uses a flexible single-column layout to adapt to all screen sizes, from mobile phones to desktops.

The calculator's internal engine performs a granular day-by-day simulation for higher accuracy, especially with complex contribution schedules. This iterative approach is reflected in the monthly plan. However, the main calculated metrics are based on the following standard financial formulas.

The final amount is the future value of the initial principal combined with the future value of a series of regular contributions (an annuity).

$$ A = P \left(1 + \frac{r}{n}\right)^{nt} + C \times \frac{\left(1 + \frac{r}{n}\right)^{nt} - 1}{\frac{r}{n}} $$

• $A$: The future value of the investment.
• $P$: The initial principal amount.
• $C$: The periodic contribution amount.
• $r$: The nominal annual interest rate (as a decimal).
• $n$: The number of times that interest is compounded per year.
• $t$: The number of years the money is invested for.

Note: This formula is a standard financial model. The calculator's day-by-day simulation may yield slightly different results depending on the timing of contributions relative to compounding dates.

Source: Investopedia: Compound Interest

Total profit is the final amount minus the initial principal. Note that in this calculator's implementation, this value also includes the sum of all additional contributions made over the term.

$$ \Pi_{total} = A - P $$

• $\Pi_{total}$: Total profit.
• $A$: Final amount.
• $P$: Initial principal.

The Effective Annual Rate is calculated using the Compound Annual Growth Rate (CAGR) formula, which measures the mean annual growth rate of an investment over a specified period of time longer than one year.

$$ R_{eff} = \left(\frac{A}{P}\right)^{\frac{1}{t}} - 1 $$

• $R_{eff}$: The Effective Annual Rate.
• $A$: The final amount (ending value).
• $P$: The initial principal (beginning value).
• $t$: The total number of years.

Note: This standard CAGR formula is most accurate for lump-sum investments without intermediate contributions. The calculator uses this as an estimate of the effective rate.

Source: Investopedia: CAGR

This is a simple projection of the monthly income you could generate if you were to withdraw only the interest earned on the final accumulated amount, based on the nominal annual rate.

$$ I_{monthly} = A \times \frac{r}{12} $$

• $I_{monthly}$: The theoretical monthly income.
• $A$: The final amount.
• $r$: The nominal annual interest rate (as a decimal).

These metrics show the average profit generated per year or per month over the entire investment term.

Average Annual Profit: $$ \bar{\Pi}_{annual} = \frac{A - P}{t} $$

Average Monthly Profit: $$ \bar{\Pi}_{monthly} = \frac{A - P}{t \times 12} $$

• $\bar{\Pi}$: The average profit (annual or monthly).
• $A$: The final amount.
• $P$: The initial principal.
• $t$: The total number of years.

The calculator supports two languages:

• English (default)
• Russian

Click the language toggle button in the header to switch between languages.

This project is built with a focus on simplicity, performance, and zero dependencies.

• Core Technologies:
  • HTML5: For the application structure.
  • CSS3: For styling, layout (Grid/Flexbox), and theming (CSS Variables).
  • Vanilla JavaScript (ES6+): For all logic, calculations, and dynamic DOM manipulation, including the SVG chart rendering.
• Development & Tooling:
  • AI-Assisted Development: The development process was significantly aided by AI coding assistants, including Qwen-Code3 and Gemini Code Assist, for generating code, refactoring, and debugging.
  • Hosting: Deployed on GitHub Pages.
• Dependencies: None. The project is entirely self-contained in a single index.html file.

• Single HTML File: Self-contained application with no external dependencies
• Pure JavaScript: No frameworks or libraries
• CSS Variables: Consistent theming and easy customization
• Event-driven Updates: Real-time calculations on input changes

• Modern Browsers: Chrome, Firefox, Safari, Edge
• Mobile Browsers: iOS Safari, Chrome for Android
• No Polyfills Required: Uses standard ES6+ JavaScript

Modify CSS variables in the :root selector to change the color scheme:

:root {
  --primary: #2563eb;        /* Main brand color */
  --primary-dark: #1d4ed8;   /* Darker variant */
  --secondary: #f8fafc;      /* Background/card color */
  --text: #0f172a;          /* Primary text */
  --text-secondary: #64748b; /* Secondary text */
  --border: #e2e8f0;        /* Border colors */
  --success: #10b981;       /* Positive values */
  --warning: #f59e0b;       /* Warning states */
  --danger: #ef4444;        /* Negative values */
}

• Grid layouts can be modified in the .calculator and .results-grid classes
• Spacing can be adjusted with padding/margin properties
• Breakpoints are defined in media queries

• No Data Collection: All calculations happen in the browser
• No External Requests: No network calls or data transmission
• Local Processing: 100% client-side computation
• No Tracking: No analytics or user monitoring

• Input Validation: Sanitized numeric inputs
• Error Handling: Graceful handling of edge cases
• Local Storage: Uses localStorage to save your last entered values for convenience. This data is stored only in your browser and is not transmitted anywhere.

This calculator is provided for informational and educational purposes only. It is not intended to be financial advice. The results are based on the data you provide and may not reflect actual investment returns. Always consult with a qualified financial professional before making any investment decisions.

This project is open source and available under the MIT License.