What Is Tax-Loss Harvesting?

Most investors know that gains are taxable. Fewer use the flip side: losses reduce that bill. Tax-loss harvesting is the practice of intentionally selling investments at a loss to offset realized capital gains and lower your tax liability — while maintaining roughly the same portfolio exposure.

The one-sentence version

You sell a losing position to crystallize the loss on paper, use that loss to cancel out gains elsewhere, then immediately reinvest in a similar (not identical) asset so your portfolio keeps working.

How it works

Step 1 — Realize the loss

A loss only counts for tax purposes when you sell. An unrealized loss — one that exists only on paper — produces no tax benefit. Selling turns the paper loss into a "realized capital loss."

Step 2 — Offset gains (or income)

Realized capital losses cancel out realized capital gains dollar-for-dollar. If you sold a stock for a ₹50,000 gain earlier in the year, a ₹50,000 loss elsewhere erases the tax on that gain entirely. In many jurisdictions, if losses exceed gains, you can also deduct a limited amount against ordinary income and carry the remainder forward to future years.

Step 3 — Reinvest immediately

Here is the key move: you buy a similar but not identical asset the same day. If you sell an index fund tracking the Nifty 50, you might buy a fund tracking the Nifty 100 or an equivalent broad-market ETF. Your capital stays in equities; you never miss a trading day; but you have harvested the tax loss.

The wash-sale constraint

Most tax codes include a rule that voids the loss if you buy the same — or a "substantially identical" — security within a short window (typically 30 days before or after the sale). Buying a close substitute sidesteps this while keeping your market exposure nearly intact.

A worked example

Suppose your portfolio holds two equity funds. During the year:

You sell Fund A and owe tax on ₹40,000 of gains. Now you also sell Fund B, realizing a ₹15,000 loss. Net taxable gain drops to ₹25,000. You immediately buy Fund C — a different mid-cap index with nearly identical sector weights. Your equity allocation is unchanged; your tax bill is ₹15,000 × (your capital gains rate) smaller.

Why it matters

The benefit compounds over time. Each harvested loss you carry forward offsets future gains, effectively deferring tax and giving that money more years to compound. Studies on taxable US portfolios estimate tax-alpha of 0.5–1.5% per year from systematic harvesting — a real edge that requires no market prediction.

It matters most in three situations:

1. High-gain years — when you have realized large profits from selling a business, property, or concentrated position.
2. Portfolio rebalancing — when you are selling to rebalance anyway; harvesting turns a neutral event into a tax credit.
3. Volatile markets — short-term drawdowns create harvesting opportunities even in broadly rising markets.

Common mistakes

• Buying the identical security too soon. Triggers the wash-sale rule and disallows the loss. Wait the required window, or switch to a genuine substitute.
• Harvesting short-term losses against long-term gains. Short-term and long-term gains are taxed at different rates. Match like with like — short-term losses offset short-term gains first.
• Ignoring transaction costs. On small positions, brokerage fees can exceed the tax saved. Harvest only when the math favours it.
• Treating it as a tax elimination strategy. It defers and reduces tax; it rarely eliminates it. When you eventually sell the substitute, the lower cost basis means a larger gain — but paying later is almost always better.

Try this

Pull up your portfolio today and filter for any position down more than 10% from your purchase price. For each one, ask: do I have a realized gain this year that this loss could offset? If yes, check whether a genuine substitute exists. If the numbers work, the trade takes ten minutes. Log the rationale and the substitute ticker in your investing research notes so you can track the 30-day wash-sale window automatically.

Related: [What is portfolio rebalancing?](./what-is-portfolio-rebalancing.md) · [What is compounding?](./what-is-compounding.md) · [The investing decision journal](./the-investing-decision-journal.md)