Start with who pays what
A bill may serve a whole household while your worksheet describes only part of it. Make that distinction visible. Record the total shown on the bill, the amount you actually pay, and the period it covers. Avoid assigning the same cost to several lines merely because it appears in more than one person’s records.
Keep changes beside the old arrangement
If the way an expense is shared has changed, date the change and retain supporting information where available. A recent move, altered household contribution, or different billing arrangement can make an older average misleading. Write a short explanation instead of forcing the new situation into an old figure. This is preparation for questions; it does not tell you what a tax authority will allow.
Bring the explanation with the evidence
For a tax-relief discussion involving finances, ask which household details are relevant and how they should be documented. Provide only the records requested through a confirmed secure process. Keep a copy of the worksheet you supplied, including its assumptions. If another household member’s information is involved, consider what permission and handling arrangements are appropriate before sharing it. Clear notes help distinguish the household’s total spending from the part your own budget actually reflects.