Capital Gains Tax Optimizer & Portfolio Simulator 2026

About This Tool

Import positions from supported brokerages or enter them manually. Simulate trades across your full portfolio and see how buying or selling affects your taxes, including wash sale warnings.

Portfolio Sources

Combine multiple brokerages by importing each source into one portfolio.

Data source

Upload Fidelity positions and lot details via CSV.

Import mode

Add to existing portfolio (combine brokerages)

New imports reset simulated trades to keep calculations accurate.

Saved Portfolio Scenarios

Save your portfolio presets and return anytime to refine your simulations.

Choose a sign-in method

Need help?

Drag & drop your Fidelity positions CSV here

or click to browse files

No Portfolio Loaded

Upload your positions CSV to get started with the simulation.

How to Use the Portfolio Simulator for Tax Loss Harvesting & Tax Optimization

This free tool helps you optimize your investment taxes through strategic planning and tax loss harvesting. Import your brokerage exports and simulate trades before you execute them. See how each trade affects your capital gains taxes, identify opportunities to harvest losses, and avoid costly wash sale mistakes.

Tax Loss Harvesting: Reduce Your Capital Gains Tax Bill

Tax loss harvesting is a strategy where you sell investments at a loss to offset capital gains and reduce your tax liability. The portfolio simulator helps you:

Identify loss positions - See which holdings are below your cost basis
Calculate tax savings - Estimate how much you'll save by harvesting losses
Avoid wash sales - Get automatic warnings if you violate the IRS 30-day wash sale rule
Optimize lot selection - Choose which tax lots to sell for maximum tax benefit (FIFO, LIFO, or specific lot)
Plan year-end strategy - Simulate different scenarios to minimize your annual tax bill

Use this tool throughout the year, especially before year-end, to proactively manage your investment taxes and maximize after-tax returns.

Step 1: Export from your brokerage

Export a CSV from your brokerage. Fidelity users can go to Positions →Download. Robinhood users can download Account Activity as CSV fromStatements & History. More brokerages are coming soon.

Step 2: Upload Your CSV

Drag and drop your CSV file or click to browse. You can import multiple sources to aggregate a combined portfolio, and the simulator will parse each supported export.

Step 3: Simulate Trades & Optimize Taxes

Click on any position to simulate a buy or sell order with full tax analysis. The simulator shows:

Lot-level breakdown - See each tax lot with cost basis, purchase date, and holding period
Short vs long-term gains - Know your tax rate (0-37% vs 0-20%) before you sell
Tax loss harvesting opportunities - Identify positions trading below cost basis to harvest losses
Wash sale warnings - Automatic detection if your trade violates the IRS 30-day wash sale rule
Tax impact estimate - See capital gains/losses and approximate tax owed or saved
Lot selection methods - Choose FIFO, LIFO, or specific lot to minimize taxes

Use the simulator to plan tax-efficient portfolio rebalancing, harvest losses before year-end, and avoid wash sales that would disallow your tax deductions.

2026 Capital Gains Tax Rates

Understanding capital gains tax rates is essential for tax-efficient investing. The rate you pay depends on how long you held the investment and your taxable income.

Short-Term Capital Gains (held 1 year or less)

Short-term capital gains are taxed as ordinary income at your marginal tax rate (10%-37% for 2026). This includes day trades, swing trades, and any stock sold within 12 months of purchase. RSU shares sold immediately at vesting are also subject to short-term rates if the gain exceeds your cost basis.

Long-Term Capital Gains (held more than 1 year)

Long-term capital gains benefit from preferential tax rates: 0%, 15%, or 20% depending on your income. Most taxpayers pay 15%. High earners (above $533,400 single / $600,050 married filing jointly in 2026) pay 20%, plus a potential 3.8% Net Investment Income Tax (NIIT).

Tax Loss Harvesting to Offset Capital Gains

Capital losses offset capital gains dollar-for-dollar. If your losses exceed your gains, you can deduct up to $3,000 per year against ordinary income, with the remainder carrying forward to future years. The portfolio simulator helps you identify and plan these harvesting opportunities while avoiding wash sale violations.

Privacy & Security

Your data stays local unless you save a scenario. By default, all processing happens in your browser. If you choose to save a scenario while signed in, we store your inputs securely so you can return and continue later.

Capital Gains Tax Optimizer & Portfolio Simulator