A plan says the file will arrive on Tuesday. Nobody has confirmed Tuesday; it was simply the date used to get the work moving. Without a label, that assumption can become a promise other people rely on.
Write the assumption and its consequence
Use a short entry: assumption; why it matters; who can confirm it; when it needs checking. You do not need a separate system for every small uncertainty.
An illustrative entry might read: “Assume data arrives Tuesday. If later, the review draft moves by the same delay. Ask the data owner before Monday afternoon.”
Separate uncertainty from a blocker
Some work can proceed under a stated assumption. Other decisions need confirmation first. Identify which case applies rather than treating every unanswered question as either harmless or fatal.
When the assumption is confirmed or disproved, update the entry and the affected plan. Leaving an outdated note beside a revised schedule can confuse the next reader.
Share the material ones
Report assumptions that could change cost, scope or delivery. Avoid overwhelming colleagues with every trivial preference.
Our guide to explaining a time estimate shows why conditions belong beside dates. An assumption log is useful when it makes those conditions visible and leads to a timely check, rather than becoming another document nobody reads.