Tax-Loss Harvesting Playbook for Q4 2025

Step 1: Inventory the unrealised losses

Run a portfolio export from your custodian and sort by largest unrealised loss. Focus on positions you can replace with similar—but not “substantially identical”—holdings to avoid the wash-sale rule.

Step 2: Model the tax savings

For each proposed sale, plug the loss amount into Scenario B of the planner. Set the "Hypothetical loss harvesting" field to the combined dollar value. The summary box shows you how much the loss reduces your total tax when paired with an upcoming gain.

Example

• Long-term gain expected: $85,000
• Harvested long-term loss: $25,000
• Federal tax savings at 15%: $3,750
• State tax savings at 5%: $1,250

Step 3: Avoid wash sales

You can buy a similar ETF or mutual fund, but avoid repurchasing the same security within 30 days before or after the sale. Track replacement trades in a spreadsheet so you can prove compliance.

Bonus idea: Harvest short-term losses first

Short-term losses offset short-term gains, which are taxed at higher ordinary rates. Use the calculator’s disposal breakdown to identify which positions will generate the largest ordinary tax reduction.

Your end-of-year checklist

• [ ] Pull realised and unrealised gain reports from every brokerage.
• [ ] Identify replacement investments before selling.
• [ ] Update the scenario planner after trades settle to confirm the new tax outlook.
• [ ] Document everything for your CPA.