Tax-Loss Harvest Optimizer

What It Does

Paste lot-level positions (one row per purchase), set your tax brackets and harvest target. Get a per-lot plan:

• HARVEST (green) — sell at a loss, the loss is deductible
• WASH (yellow) — sell would trigger wash-sale, loss disallowed
• HOLD (grey) — at a loss but the target has already been met
• GAIN (blue) — holding avoids realizing a taxable gain

Plus aggregate stats: lots to sell, total losses harvested, ST vs LT split, federal tax saved, carry-forward beyond the $3,000/yr cap.

Input format

CSV with these columns (case-insensitive, synonyms recognized):

Required	Aliases
ticker	symbol, sym, stock
buy_date	date, purchase_date, acquired
shares	quantity, qty, units
cost_per_share or cost_basis	price, cost, unit_cost, avg_price (or basis aliases)
current_price	current, market_price, last

ticker,buy_date,shares,cost_per_share,current_price
AAPL,2024-03-15,100,170.50,225.00
TSLA,2024-01-10,40,400.00,180.00
VOO,2024-06-20,80,490.00,560.00

Optionally paste a “recent transactions” CSV for the last 60 days — buys there get cross-checked against the wash-sale window.

Wash-sale rule

IRC §1091: if you sell a security at a loss and you (or your spouse, or any account you control including IRAs) buy a substantially identical security within 30 days before or after the sale, the loss is disallowed. Instead, the disallowed amount is added to the cost basis of the replacement shares — you eventually get the benefit, but the harvest year’s deduction is gone.

This app’s detection scope:

Detected	How
✅ Same-ticker buy within ±30 d of today (from your positions)	Direct match in the lot list
✅ Same-ticker buy in the recent-transactions CSV	Direct match in optional input
❌ Spouse / IRA / 401(k) purchases	You’d have to add them to the recent-tx CSV
❌ ETFs tracking the same index (SPY vs VOO vs IVV)	Listed in the replacement panel for your judgment
❌ Options / warrants of the same underlying	Out of scope
❌ Sales placed in the future	”Today” is the reference point — set the reference date if you’re planning ahead

The IRS hasn’t published a definitive list of what counts as “substantially identical.” Most tax pros treat SPY/IVV/VOO as not substantially identical (different funds, different sponsors), but two share classes of the same fund clearly are. The replacement panel surfaces commonly-cited pairings — verify with your tax advisor.

Tax assumptions

Short-term rate defaults to 24% (the 2026 federal marginal for ~$100K-$200K MFJ income). Pick yours.

Long-term rate defaults to 15% (the standard bracket for most filers). Choose 20% for high earners or 23.8% if you also pay the 3.8% Net Investment Income Tax.

$3,000 cap: federal rules let you deduct at most $3,000 of net capital losses against ordinary income per year. Excess carries forward indefinitely (still useful for offsetting future gains). The plan shows the carry-forward amount.

Federal-only: state-tax overlay is deliberately out of scope for v1 because state conformity to federal cap-gains treatment varies wildly (CA partial, NJ no LT preference, NH/TN no income tax) and getting it wrong would mislead. Add the state delta manually if you need it.

What’s NOT Included (intentional)

• Trade execution — never. The app produces a plan; you review and place trades in your brokerage. This is a hard rule.
• Broker integration — same reason
• Real-time prices — paste your current prices; if you want live quotes write your own ETL into the CSV
• State-tax overlay — see above
• Cross-account aggregation — your spouse’s IRA can trigger wash-sale on your taxable account. Either add those buys to the recent-tx CSV or remember to check manually
• Options / futures handling — equities only for v1
• Persistent state — reload starts fresh, by design

Related Tools

• Amortization Calculator - the other big finance app
• Position Sizer - position sizing math (Kelly criterion, fixed fractional)
• Options P&L Visualizer - if your harvest involves options legs
• Drawdown Calculator - max drawdown from a return series