How to choose a travel cost calculator
Use a travel budget calculator or holiday budget calculator when the question is how much a trip will cost before booking. Those tools focus on flights, accommodation, food, local transport, activities, insurance, exchange-rate assumptions, and a contingency buffer.
Use a holiday cost per person calculator when the main question is how to split group costs fairly. Use a holiday spending money calculator when the booking is already handled and the remaining question is daily meals, local transport, cash, and activities. Use a travel tipping calculator when the extra amount depends on a bill, service category, and destination-style convention.