Budget an anniversary celebration.
An anniversary celebration has one cost that scales with guests and several that do not. Catering is per head and therefore the term that decides whether the guest list grows or shrinks; venue hire, photography and the gift are largely fixed. Splitting them shows the marginal cost of an extra guest, which is the catering figure alone — usually far less than the all-in per-guest number, and worth knowing when someone asks to bring a partner. The contingency is worth carrying because celebration budgets fail at the edges: extra bar tab, a cake upgrade, transport, and the flowers nobody costed.
Anniversary Celebration Budget
Catering = guests x per-guest cost; subtotal = venue + catering + gift + photography; total = subtotal x (1 + contingency%)
The catering rate, not the all-in per-guest figure. Venue and photography do not change, so an extra guest at 32 dollars catering costs 32 dollars, not the 60 or 70 the average suggests.
Ten percent for a straightforward gathering and 15-20% for anything with a venue, suppliers and a bar, where small overruns compound across several vendors.