Why You Should Keep a Decision Log (and a Simple Format to Start With)

Disclosure: this post was written with AI assistance and reviewed before publishing.

Six months after an important decision, most teams can tell you what they decided but not why. The context — the options considered, the constraints at the time, the assumptions — disappears. A decision log is a lightweight way to keep it. It's useful for teams and solo founders alike, and it takes a couple of minutes per decision.

What a decision log gives you

• Memory. New team members can understand why things are the way they are.
• Fewer repeated debates. When someone asks "why don't we just…?", you can point to the entry, and reopen it only if something has changed.
• Better judgement over time. Reviewing past decisions against outcomes shows where your reasoning tends to be good or weak. A good decision can still have a bad outcome due to luck; the log helps you tell the difference.
• Accountability without blame. It's clear who decided and on what basis.

Software teams have long done a version of this with Architecture Decision Records (ADRs). The same idea works for product, marketing, hiring and finance decisions.

What deserves an entry

Log decisions that are:

• Hard to reverse (pricing changes, contracts, hiring, technology choices)
• Expensive in money or time
• Likely to be questioned later
• Made under uncertainty, where you want to check your assumptions afterwards

Don't log everything. If an entry would take longer than the decision itself, skip it.

A simple format

ID: D-014
Date: 2026-10-14
Decision: Move from monthly to annual-only pricing for the Pro plan
Status: Accepted   (Proposed / Accepted / Superseded by D-0xx / Reversed)
Decider: Maria (with input from Jon, Priya)

Context:
  Churn on monthly Pro is high; support load from billing issues is growing.

Options considered:
  1. Keep monthly + annual
  2. Annual only, with a discount
  3. Monthly only, with a price increase

Reasoning:
  Option 2 reduces billing churn and support load; risk is lower conversion.

Assumptions:
  - Conversion drops by no more than 20%
  - Support tickets about billing fall noticeably

Review date: 2027-01-15
Outcome (filled in at review):

The assumptions and review date are what make the log more than a diary. They turn each decision into a small, checkable prediction.

Where to keep it

Anywhere searchable and shared:

• A spreadsheet with one row per decision
• A Notion or similar database with properties for status, decider, area and review date, plus a page body for the full reasoning
• Markdown files in a repository for technical teams (the ADR approach)

The tool matters less than having one agreed location. Link to the entry from wherever the decision was discussed (meeting notes, tickets, chat).

Building the habit

• Make it part of the decision meeting. The last item: "Who's writing the log entry?"
• Keep entries short. Ten lines is plenty for most decisions.
• Write it when you decide, not weeks later; context fades quickly.
• Use a template so nobody starts from blank.

Reviewing decisions

Set a recurring reminder — monthly or quarterly — to look at entries whose review date has passed. For each:

1. What actually happened?
2. Were the assumptions right?
3. Was the reasoning sound given what we knew then?
4. Would we decide the same way again?

Record the outcome in the entry. If the decision changes, don't edit the original: create a new entry and mark the old one as superseded. That preserves the history.

Common mistakes

• Logging only the decision, not the options and reasoning
• No review date, so nothing is ever checked
• Editing old entries instead of superseding them
• Storing the log somewhere nobody looks
• Logging trivial decisions until the habit becomes a chore

Summary

Record important, hard-to-reverse decisions in a short, consistent format that includes context, options, reasoning, assumptions and a review date. Keep it in one searchable place, write entries at decision time, and review them against outcomes. A few minutes per decision builds a memory your team can actually use.

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If you'd rather start from a ready-made structure, I put together a small, inexpensive, AI-assisted kit on this topic: Decision log systems. There's a *free sample** (the intro plus one complete template), so you can check whether it's useful before paying anything. Everything above works without it. Other kits: all products.*

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