@CDR52023 asking about 2026 is a little far out for IRMAA, but this is the best website I have found that attempts to estimate it (it goes out through 2025 currently and I suspect will add 2026 in a few months)
https://thefinancebuff.com/medicare-irmaa-income-brackets.html
Even the 2025 IRMAA brackets are not 'locked in' as it is predicated on the inflation adjustment from Sept 2023 - Aug 2024. That is one of the "annoying' things about IRMAA. While your AGI will be locked in on Dec 31, 2023, only 4 of the 12 inflation numbers that 'lock in' the 2025 IRMAA brackets will be known. It is exasperating!
this website has estimated 2024 tax brackets among a number of other estimates for 2024.
https://pro.bloombergtax.com/reports/2024-projected-u-s-tax-rates/
