Expiry date is always 31st March. In your case, 2026
2026 or 2027-March
In 2025, I'm at 64 nights (60 carryover + Dec 31 to Jan4), so 60 nights attained in 2025 which gives remainder of year attaining 60 nights and the following year 2026 ....then as you say it goes to March 31...thus 2027
Had similar thing with IHG with 140 nights in 2023, 70 nights carried over in 2024, thus have Diamond to end 2025