Short answer: For a classic luxury Sri Lanka trip (south/coast + hill country + safaris + whale-watching), the best overall window is December–March — best weather across the southwest coast and central hills, calm seas, excellent whale watching, and full access to luxury resorts. If you want the east coast (secluded, top surf & beaches) choose May–September. For peak safari viewing in the south/east, aim for February–June. (sno.com)

Details and how to pick by interest

• Beaches & luxury resorts (Galle, Mirissa, Bentota, Colombo): Best November–April (dry, calm seas, ideal for beach resorts, private villas and watersports). Peak demand and prices sit in Dec–Jan. (sno.com)
• Whale and dolphin watching (Mirissa / southern waters): Best roughly December–April (blue whale season peaks around Feb–Mar). Great for private charters and luxury viewing trips. (thetimes.co.uk)
• Hill country (Nuwara Eliya, Ella, tea-estate luxury lodges): Best December–March for cool, clear days and scenic views. Ideal to combine with five-star train journeys and high-end tea estate stays. (sno.com)
• Wildlife safaris (Yala, Udawalawe, Wilpattu): Best wildlife viewing in the dry months — broadly February–June (animals concentrate at waterholes). Note Yala has seasonal closures/maintenance in some blocks (September) and variable local timing — check park notices when booking. (yalalk.com)
• East coast (Trincomalee, Nilaveli, Arugam Bay): Best May–September — ideal for quiet, luxury beach camps, surfing Arugam Bay and calm eastern beaches. (sno.com)

When to travel for the best luxury value and experience

• If you want perfect weather and don’t mind peak prices: December–March. Book 3–6+ months ahead for top villas and boutique hotels (holiday weeks around Christmas/New Year fill quickly). (sno.com)
• If you prefer fewer crowds but still excellent conditions: February–March or November (shoulder months offer slightly lower rates and great weather). (thetimes.co.uk)
• If you want a “green” luxury trip (lush landscapes, lower rates): consider the monsoon shoulder months — but accept occasional rain and region-specific planning. (sno.com)

Special events to consider

• Kandy Esala Perahera (big cultural procession): held in July–August — spectacular if you want a culturally rich luxury stay in Kandy, but not optimal for southwest beach weather. (en.wikipedia.org)
• Adam’s Peak pilgrimage season: December to mid‑April — popular for luxury travelers who combine a guided night climb with boutique stays. (thetimes.co.uk)

Quick practical tips for luxury travelers

• Combine regions: fly domestic (short hops) between coast / hill country to maximize time in five-star properties.
• Private transfer and bespoke guides: highly recommended for safaris, cultural sites and whale charters.
• Book prime experiences early: private yacht/charters, boutique villas, and popular luxury train cabins are limited in peak season. (thetimes.co.uk)

If you tell me which part of Sri Lanka you most want to prioritize (beaches, whales, private-safari, tea-country luxury, or a combination), I’ll tailor an ideal month/window and a short luxury itinerary with booking tips.