Quick answer
Split every cost into fixed and per-head. Divide your total by the guest count to find your real per-person figure, then treat every addition to the guest list as that number rather than as "one more chair".
Fixed costs and per-head costs behave differently
A photographer costs the same for eighty guests as for a hundred and twenty. Catering, drinks, place settings, favours, transport and often venue staffing do not. Mixing the two into one list of line items is what makes a budget feel unmanageable, because half of it moves whenever the guest list does and half of it does not.
Work out your real per-head number
Add up everything that scales with guests, divide by your current headcount, and be honest about what belongs in there — food, drinks, cake, hire per cover, stationery, favours, and the transport that scales. That single figure is the most useful number in the whole budget, because it prices every subsequent guest list conversation.
Then use it as a decision tool
When someone suggests adding four more people, the answer is not "we will see" — it is four times the per-head figure. That converts an emotional negotiation into an arithmetic one, which is much easier to have with family.
Categories worth having
- Venue and hire
- Food and drink
- Attire and beauty
- Photography and video
- Flowers and styling
- Music and entertainment
- Stationery and invitations
- Transport and accommodation
- Rings, gifts and favours
- Contingency
Contingency is not optional
Keep roughly ten per cent unallocated. It will be spent — on the thing the venue does not include, the supplier who charges for travel, the alterations, the second cake. A budget with no contingency does not avoid those costs, it just discovers them as failures.
Track three numbers per line, not one
Estimated, committed and paid. A deposit paid on a venue is a very different state from a quote you have accepted or a figure you invented in January, and a budget that only tracks "spent" tells you nothing about what you have already promised.
Keep the receipts with the line
Attaching the invoice to the expense means the answer to "what did we agree with the florist" is one click rather than an archaeology expedition through an inbox. It matters most at exactly the moment you have least patience for it.
Let the headcount update the budget
The advantage of tracking a budget in the same place as the guest list is that per-head totals recalculate as RSVPs arrive. Inviterio's budget tracker sits on the paid plans and does exactly this — the catering line follows the confirmed headcount instead of the number you typed in six months ago.