Pure Benchmarks · Guide

How Do I Review My Past Investment Decisions?

Short answer

An investment post-mortem reviews a past decision in four steps: restate what you knew and expected at the time, measure what the decision was worth against the alternative of not making it, compare that with what you expected, and separate what was within your control from what was luck. Write the review down and look across several decisions rather than one. The aim is not to find blame but to learn which parts of your process work, so the next decision is better regardless of how the last one turned out.

Most investors look back at a trade only when it went badly, and then mostly to feel bad about it. A structured post-mortem turns that into something useful: a repeatable way to learn from every decision, good and bad. This page lays out a step-by-step review, the questions worth asking, the traps that make reviews misleading, and how to put a fair number on what each decision was worth.

Step 1: restate the decision as it was

Write down what you did, when, and why, using what you knew at the time. If you kept a decision journal, start from that entry. If not, be careful: memory tends to rewrite reasons to fit the outcome. Include what you expected to happen and over what period.

Step 2: measure the result against doing nothing

The fair comparison for most changes is the portfolio you would have had without them, carried forward on real prices. Comparing with an index mixes in your allocation; comparing with your hopes mixes in hindsight. A decision benchmark, the frozen pre-change portfolio, isolates the effect of the change itself.

Step 3: compare result with expectation

Did the decision work for the reason you gave? A stock bought for earnings growth that rose on a takeover rumour worked, but not because of your thesis. A sale made to reduce risk that lagged a rally may still have done its job. Matching the result to the reason tells you whether your process is being rewarded.

Step 4: separate skill from luck

List what was within your control, such as research, sizing, timing rules and costs, and what was not, such as market moves and surprise news. A single result cannot settle the question; patterns across many reviewed decisions can. Avoid outcome bias by giving the process its own grade, independent of the result.

Making reviews routine

A post-mortem is most useful when it is regular and covers every decision, not only the painful ones. Pure Benchmarks, our own product, supplies step 2 automatically: its Decision Benchmark scores every buy and sell in linked accounts against the do-nothing portfolio, so each review starts from a measured result rather than a recollection.

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Frequently asked questions

What is an investment post-mortem?

It is a structured review of a past decision: what you knew, what you did, what it was worth against not doing it, and what you can learn.

How often should I review my investment decisions?

Many investors review once or twice a year as part of a portfolio review, covering every change rather than only the ones that went badly.

What should I compare a past decision against?

For most changes, the portfolio you would have had without the change, carried forward on real prices. That isolates the decision from the market.

How do I avoid hindsight bias in a review?

Use reasons recorded at the time, ideally in a decision journal, and grade process and result separately.

Is there a tool that measures my past decisions?

Pure Benchmarks, our own product, scores each change in linked accounts against the do-nothing baseline. This page is information for comparison and not a recommendation about any holding.

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This page is an information baseline for comparison only. It is not investment advice and not a recommendation to buy, sell, replace, or transfer any specific asset, account, or firm. Past performance does not guarantee future results. All figures shown are illustrative.