If you understand a small handful of tax-code concepts, most of tax-aware portfolio management stops looking mysterious.
This is the practical cheat sheet. Not every rule in the code matters equally. These are the ones that keep showing up in real TLH, direct indexing, and overlay decisions.
The four sections that matter most
Which sections of the U.S. tax code matter most for tax-loss harvesting and direct indexing decisions?
Four code sections cover the core terrain: §1091 (wash-sale rule), §1014 (basis step-up at death), §1233 (short-sale character), and §1259 (constructive sales) — together they determine whether a harvest is usable, a hedge is clean, and a long-horizon plan actually works.
| Section | What it governs | Why investors care |
|---|---|---|
| §1091 | Wash sales | Determines whether a harvested loss is actually usable |
| §1014 | Basis step-up | Changes the long-term value of deferral and holding appreciated assets |
| §1233 | Short-sale character | Matters for any strategy that introduces a short overlay |
| §1259 | Constructive sales | Prevents certain offsetting trades from avoiding gain recognition |
§1091, the wash-sale rule
What does §1091 say, and why does it shape every tax-loss harvesting decision?
IRC §1091 disallows a capital loss when the same or substantially identical security is purchased within 30 days before or after the sale — creating a 61-calendar-day danger window that separates real harvesting from ineffective harvesting.
This is the rule most investors have at least heard of, usually in a very incomplete way.
The basic issue is simple: if an investor sells at a loss and buys the same or substantially identical security inside the relevant window, the loss is disallowed.
Why it matters: this is the rule that separates real harvesting from fake harvesting. If a product cannot handle wash-sale logic competently, it is not serious.
Read the deeper article here: The wash-sale rule, demystified.
§1014, basis step-up
How does the §1014 basis step-up change the long-run economics of holding appreciated assets?
Under IRC §1014, inherited assets generally receive a new cost basis equal to fair-market-value at the relevant transfer date — a rule that can eliminate decades of embedded gains and makes long-horizon hold decisions far more valuable than a one-year tax view suggests.
This is the long-horizon rule investors tend to underweight. Basis step-up is one of the reasons deferral can be far more valuable than it first appears.
Why it matters: investors should not think about tax-aware investing only in one-year increments. The estate path can change the real economics substantially.
Read the deeper article here: The step-up in basis.
§1233, short-sale character
What does §1233 govern, and why does it matter when a short overlay is added to a portfolio?
IRC §1233 determines how the holding period and tax character of short-sale gains and losses are treated — rules that differ meaningfully from ordinary long-only holdings and change the tax profile of any portfolio that introduces a short sleeve.
This is where things start to matter for more advanced structures. Short positions are not taxed the same way as ordinary long-only holdings, and anyone discussing a short overlay needs to understand that the character of gains and losses behaves differently.
Why it matters: adding a short sleeve changes not only the market exposure of the portfolio — it also changes the tax character conversation.
§1259, constructive sale
What is a constructive sale under §1259, and when does it create an unexpected tax event?
IRC §1259 treats certain closely offsetting positions — such as a long holding paired with a substantially offsetting short — as a constructive sale that can trigger gain recognition, blocking some attempts to neutralize a gain without an immediate tax consequence.
This is one of the rules that blocks naive attempts to "hedge without consequences" in certain cases. If an investor is trying to neutralize a gain with a tightly offsetting position, the constructive-sale concept can matter a lot.
Why it matters: sophisticated-looking overlays can create tax recognition if the system is not designed carefully.
The supporting concepts worth remembering
Beyond the four primary code sections, which adjacent tax concepts most affect what an investor can do with harvested losses?
Capital-loss carryforwards, holding period (short-term vs long-term character), retirement-account boundaries, and charitable donation of appreciated assets all shape the downstream value of any harvesting strategy.
There are also adjacent rules and concepts that are not always the headline, but still matter:
- capital-loss carryforwards
- short-term versus long-term character
- retirement-account boundaries
- charitable donation of appreciated assets
These are not side notes. They shape what a user can actually do with the losses they generate.
Why this matters for software
Why does a serious tax-aware product need to reason about these code sections on every proposed trade?
A real tax-aware product is a rule-checking system — every proposed trade must be evaluated against wash-sale windows, gain-and-loss character, and constructive-sale constraints, not just price and return data; HarvestEngine's rule engine handles this check on each proposal.
Every proposed trade should be able to answer questions like:
- does this create a wash-sale problem
- what kind of gain or loss character is involved
- does this collide with a more advanced constructive-sale issue
- how does this fit into the user's broader tax path
That is why HarvestEngine is designed as a portfolio operating system, not just a signal feed.
The honest takeaway
What is the practical takeaway for investors who want to use tax-aware strategies without becoming tax lawyers?
A small set of code sections — §1091, §1014, §1233, and §1259 — determines whether any given tax-aware move is productive, neutral, or counterproductive; understanding those four concepts is the useful threshold for most investors.
Most investors do not need to memorize code sections. They do need to understand the handful of rules that keep determining whether a tax-aware move is smart, neutral, or counterproductive.
That is the point of this cheat sheet. It turns the legal scaffolding into something operational.
Read this next with TLH 101, the wash-sale explainer, the step-up article, and AMT and harvested losses.