# Investment Calculator

> Fast, private, client-side investment calculator that computes real wealth in today's purchasing power after fund expense ratios, capital gains tax, and inflation.

## Primary Canonical URL
https://YOURDOMAIN.com/

## Key Financial Capabilities
- **Real Returns vs Nominal Returns**: Distinguishes between paper nominal ending values and real purchasing power adjusted for compound consumer price inflation.
- **Erosion Decomposition ("What's eating your returns?")**: Computes exact dollar and percentage losses caused by annual fund management fees (expense ratios), exit taxes, and inflation.
- **Combined Lump Sum & Monthly SIP**: Simulates an initial capital deposit combined with recurring monthly contributions.
- **Annual Step-Up**: Simulates annual percentage increases in monthly contributions (e.g. 5% to 10% per year) matching career earnings growth.
- **Goal Seeking Mode**: Employs an exact binary search solver across a period-by-period monthly loop to identify the exact monthly contribution required to reach any target net worth.
- **CAGR vs XIRR**: Solves for internal rate of return (XIRR) on multi-date recurring cash flows alongside point-to-point CAGR.
- **100% Client-Side Privacy**: Runs in the browser without server storage, tracking, or login requirements.

## Mathematical Formulas
- **Net Annual Return**: `r_net = r_gross - fee_annual`
- **Compounding Periodic Rate**: `r_period = r_net / (periods_per_year)`
- **Timing (End of Period vs Start of Period)**: End of period deposits (ordinary annuity) accrue interest on existing balance; start of period deposits (annuity due) accrue interest on balance + new contribution.
- **Capital Gains Tax**: `tax = max(0, ending_balance - total_invested) * tax_rate`
- **Real (Inflation-Adjusted) Value**: `real_value = (ending_balance - tax) / (1 + inflation_rate)^years`
- **Fee Opportunity Drag**: `fee_drag = gross_balance_without_fees - net_balance`

## Common Benchmarks
- Conservative Return Baseline: 4% – 6% (bonds / cash / defensive assets)
- Balanced Return Baseline: 6% – 8% (global equities, 60/40 or 80/20 portfolios; recommended starting default: 7.0%)
- Aggressive Return Baseline: 9% – 11% (100% large-cap equities, e.g. S&P 500)
- Long-term Average Inflation: 2.5% – 3.0%
- Typical Low-Cost Index ETF Expense Ratio: 0.03% – 0.20%

## URL Query Parameter Interface
Users can bookmark and share specific scenarios using query parameters:
- `mode`: "forecast" or "goal"
- `init`: initial lump sum number (e.g. `10000`)
- `monthly`: monthly contribution number (e.g. `500`)
- `stepUp`: annual step-up percentage (e.g. `10`)
- `years`: investment horizon in years (1 to 50, e.g. `20`)
- `return`: expected annual return rate % (e.g. `7`)
- `fee`: annual expense ratio % (e.g. `0.5`)
- `inf`: annual expected inflation rate % (e.g. `3`)
- `tax`: capital gains tax rate % (e.g. `15`)
- `freq`: compounding frequency ("monthly", "quarterly", "yearly")
- `timing`: contribution timing ("start", "end")
- `curr`: currency code (e.g. "USD", "EUR", "GBP", "INR", etc.)
- `target`: wealth target when mode="goal"