1. Start with two budgets, not one total
Expected spend is the sum of items you are likely to buy: the flight currently on sale, a real shortlist of stays, daily meals and planned transport. Mixing in vague shopping money hides the true cost difference between routes.
The itinerary planner's default 5% is a route-change comparison buffer. Before departure, you can separately set available card and cash funds at a conservative 10% above expected spend. Confirmed baggage or seat charges belong in expected spend, not in either reserve.
2. Price flights and stays by their real billing units
For flights, add adult and child fares, checked baggage, seats and airport access separately. Compare carriers with the same baggage allowance because the headline fare is rarely the final payment.
Stays are billed per room-night, not per traveler, so label taxes and breakfast explicitly. A split stay—Nha Trang city and Cam Ranh, or Da Nang and Hoi An—also creates transfer and luggage-handling costs on changeover day.
3. Build food and local transport from daily rates
Check whether breakfast is included, then place local meals, cafés and booked restaurants into each daily route. Pricing the type of meal you will actually eat avoids both bargain-only and premium-only distortions.
Separate the one-way airport ride, cross-zone journeys and short rides within a neighborhood. Do not multiply a shared car fare by every passenger; multiply only true per-person fares such as bus tickets.
4. Check adult-child rules and what each experience includes
Child pricing for tours and attractions may depend on age, height or whether a seat is occupied. A family budget should give children their own line instead of applying the adult rate to everyone.
Confirm whether pickup, admission, meals and equipment are included. For products such as Mui Ne dune tours, where transport inside the dunes may cost extra, list the base product and optional charge separately.
5. Compare cities with identical trip assumptions
For a five-day comparison, hold the departure airport, baggage, hotel level, party size and number of experiences constant. Change only the city's real cost drivers, such as frequent rides in Ho Chi Minh City, long island transfers in Phu Quoc or a northern day trip from Hanoi.
A single city total conceals the difference between one base and a split stay. Put flights, rooms, daily costs, long transfers and experiences side by side to see what actually drives the budget.
6. Do not add the 5% and 10% reserves together
The 5% figure is the planner's default route-change buffer for comparing hotel and activity edits. The optional 10% figure is a conservative available-funds target before departure. They are alternatives for different decisions, not a combined 15% surcharge.
Build expected spend first, use the 5% line while editing the itinerary, and—when appropriate—keep up to 10% above expected spend available across cards and cash. Shopping remains a separate optional allowance.