Is it cheaper to book a round trip or two one-way tickets?

Almost always round trip. International carriers rarely offer competitive one-way pricing for trans-pacific or trans-atlantic routes.

Does flying on a specific day of the week actually matter?

Yes. Mid-week flights (Tuesday/Wednesday) are statistically 10-15% cheaper than weekend flights.

How to Book Cheap Flights to Thailand

To get the best price, set a Google Flights alert 4 to 6 months before your departure and aim to fly into Bangkok Suvarnabhumi (BKK) rather than regional airports. Aim to book on a Tuesday or Wednesday for departures during the shoulder season months of May, June, September, or October.

Set up price tracking. Go to Google Flights, input your home airport and Bangkok (BKK). Toggle the 'Track Prices' switch on. You will receive an email whenever the price drops significantly.
Use the 'Explore' feature. If your dates are flexible, use the 'Explore' map on Google Flights. Enter your origin and 'Thailand' as the destination. It will show you the cheapest month to fly based on historical data.
Check budget airlines for the final leg. Sometimes it is cheaper to fly into a major Asian hub like Singapore (SIN) or Kuala Lumpur (KUL) on a long-haul carrier, then book a separate budget flight (like AirAsia or VietJet) into Thailand. Ensure you leave at least 4 hours between flights if not on a single ticket.
Clear your browser cache. Always use an Incognito or Private window when searching. Sites use cookies to track your interest, which can occasionally inflate prices for routes you search repeatedly.

Is it cheaper to book a round trip or two one-way tickets?: Almost always round trip. International carriers rarely offer competitive one-way pricing for trans-pacific or trans-atlantic routes.
Does flying on a specific day of the week actually matter?: Yes. Mid-week flights (Tuesday/Wednesday) are statistically 10-15% cheaper than weekend flights.