Tax Loss Harvesting Basics
Last verified: 2026-06-21
People search for tax loss harvesting basics because they want a clear answer before money, timing, or risk gets involved. The useful answer is not a prediction. It is a framework that makes the decision visible before the click and reviewable after the outcome.
This Bucko Library page is educational. It is built for research, journaling, scenario analysis, guardrails, and review. It is not personal guidance or a recommendation to buy, sell, trade, or avoid any security.
Source note: last checked IRS Topic No. 409 and IRS Publication 550 on 2026-06-21 for broad capital gain/loss and wash sale framing.
The plain-English version
Tax loss harvesting starts with a simple idea: if an investment is sold below its tracked cost basis, the realized loss may matter in the investor's tax picture. The useful part is not the word harvesting. The useful part is the process: identify the lot, understand why the position changed, avoid sloppy replacement decisions, and keep records clean enough for tax review.
The trap is thinking the loss itself is a win. A realized loss can be useful in some circumstances, but it can also create bad behavior if the investor sells only for tax optics, loses desired exposure, buys back too quickly without checking rules, or turns portfolio management into paperwork theater.
The simple math framework
Start with tax-lot math before any story:
Sale proceeds - cost basis = realized gain or loss before adjustments
Example: shares with a tracked basis of $10,000 are sold for $8,700. The pre-adjustment realized loss is $1,300. That number is not the whole answer. Account type, wash sale rules, other gains/losses, holding period, and local tax treatment can all matter.
A cleaner planning worksheet is:
Realized loss candidate
+ exposure change
+ replacement choice
+ calendar/rule review
= decision worth documenting before the trade
What beginners usually miss
- ▸Selling a weak position and accidentally changing the whole portfolio's risk profile.
- ▸Buying a replacement without understanding whether it creates rule or tracking problems.
- ▸Waiting until filing season to reconstruct basis, dates, and reasons from memory.
- ▸Letting tax language override the original investing plan.
Tax-aware investing is a recordkeeping and process problem before it is a clever tactic. The better question is not “can I harvest this?” It is “what exposure am I giving up, what am I replacing it with, and how will this look when reviewed later?”
A Bucko-style checklist
Before acting, write down:
- ▸Ticker, account, tax lot, basis, and estimated proceeds.
- ▸The reason for selling besides the tax angle.
- ▸The exposure you still want after the sale, if any.
- ▸Replacement plan and calendar/rule review notes.
- ▸The review date for confirming records and portfolio drift.
Bucko fits here as an educational research, journaling, scenario-analysis, and review workspace. Save the thesis, tag the tax-review item, track the calendar, and compare the post-sale portfolio against the original plan.
Example scenario
An investor owns a fund with a $10,000 basis and current value of $8,700. The portfolio plan still wants broad equity exposure, but the specific position is down. A rushed decision says, “sell it for the loss.” A better decision writes down the exposure target, replacement idea, timing review, and records needed for a tax professional.
The loss may matter, but the process matters more. If the investor exits exposure during a rebound or creates avoidable record confusion, the tax idea may have made the portfolio worse.
How to use this page in practice
- ▸Define the decision in one sentence.
- ▸Translate the risk into dollars, dates, exposure, or contract terms.
- ▸Compare that risk with your written limits.
- ▸Journal the reason for any change before the result is known.
- ▸Revisit the decision on a set cadence instead of only after a surprising move.