A trip budget has five buckets: transportation (flights, trains, rental car, fuel), lodging (nights x nightly rate, plus taxes and fees), food and drink (per day x days), activities and sightseeing, and a contingency buffer of 10 to 15 percent for the surprises every trip produces. The per-day method is the fastest way to build one: estimate a daily burn rate for lodging, food, and activities, multiply by days, then add the fixed costs (flights) that do not scale with trip length. Longer trips dilute the fixed costs — the flight hurts less per day on a two-week trip than a long weekend.
The categories people forget are what break budgets: baggage fees, airport transfers, parking, tips, travel insurance, visa fees, roaming charges, and the 'arrival day' effect (tired travelers overspend on day one). Taxes and resort fees can add 15 to 25 percent to a quoted hotel rate in some cities — always budget the all-in nightly price, not the headline. Track spending daily on the trip with a notes app; travelers who check the running total each evening outspend their plan far less than those who discover the damage at home.
Build the budget before booking anything, because the budget should choose the trip, not the other way around: if the math says $2,500 and the itinerary says $3,200, change the itinerary (fewer cities, cheaper lodging tier, shoulder season) rather than hoping. This calculator sums your categories and adds the contingency buffer into a single trip total.