Should I use an ATM or exchange cash?

Use an ATM. Thailand charges a flat fee of 220 THB (about $6.50) for international cards, so withdraw the maximum amount each time to minimize the impact of the fee.

Is it cheaper to book ahead or when I arrive?

For hostels and internal buses, booking 2-3 days in advance on apps like Agoda or 12Go is sufficient and keeps your itinerary flexible without overpaying.

How to budget for backpacking Thailand

Budget for $40 to $55 USD per day to cover hostels, street food, local transport, and a couple of beers. If you plan on taking domestic flights and booking private rooms, increase your daily allowance to $75 USD.

Calculate your daily base. Expect to spend $15 on a decent hostel dorm, $15 on food and water, and $10 on transport and miscellaneous costs. This is your 'survival' baseline.
Layer in the 'Fun' tax. Add $15 to your daily budget for every day you plan to do an activity, such as a snorkeling tour in the south ($25-40), a temple entry fee ($5), or a cooking class ($25).
Factor in regional pricing. Northern Thailand (Chiang Mai, Pai) is roughly 20% cheaper than the Southern islands (Phuket, Koh Samui, Phi Phi). Allocate more funds for island-hopping logistics.
Account for transport transitions. Budget an extra $50 for every long-distance move, covering sleeper trains or buses. If flying, add $70 per flight including checked baggage fees.

Should I use an ATM or exchange cash?: Use an ATM. Thailand charges a flat fee of 220 THB (about $6.50) for international cards, so withdraw the maximum amount each time to minimize the impact of the fee.
Is it cheaper to book ahead or when I arrive?: For hostels and internal buses, booking 2-3 days in advance on apps like Agoda or 12Go is sufficient and keeps your itinerary flexible without overpaying.