Sources and methodology
RetirementTaxIndex uses primary government publications for calculation constants and explanatory pages. The shared rule registry records the rule year, source of record, source publication date when available, site implementation date, and last review date.
Official source ledger
| Official source | Published | Reviewed | Use on this site |
|---|---|---|---|
| CMS: 2026 Medicare Parts A and B premiums and deductibles | November 14, 2025 | August 16, 2026 | Numerical source of record for 2026 Part B and Part D IRMAA values |
| SSA: 2026 premiums for higher-income Medicare beneficiaries | Publication year shown by agency | August 16, 2026 | Operational confirmation of filing groups, MAGI, lookback, and billing |
| IRS: Publication 915 (2025), Social Security and Equivalent Railroad Retirement Benefits | Publication year shown by agency | August 16, 2026 | Source of record for the simplified Social Security benefit inclusion method |
CMS is the numerical source of record for the 2026 Part B and Part D tables. SSA is used for operational confirmation such as MAGI, filing groups, lookback timing, notices, and billing.
Value-to-source mapping
| Rule value | Current value | Official location | Reviewed |
|---|---|---|---|
| Standard Part B monthly premium | $202.90 | CMS: Part B Premium and Deductible | August 16, 2026 |
| Part B annual deductible | $283 | CMS: Part B Premium and Deductible | August 16, 2026 |
| Individual standard-tier ceiling | $109,000 | CMS: Full Part B Coverage table | August 16, 2026 |
| Joint standard-tier ceiling | $218,000 | CMS: Full Part B Coverage table | August 16, 2026 |
| MFS lived-together middle range | Above $109,000 and below $391,000 | CMS: Married filing separately table | August 16, 2026 |
| Part D income-related additions | $0.00 to $91.00 monthly | CMS: Part D table | August 16, 2026 |
| Individual base and upper amounts | $25,000 and $34,000 | IRS: Base amount and worksheets | August 16, 2026 |
| Joint base and upper amounts | $32,000 and $44,000 | IRS: Base amount and worksheets | August 16, 2026 |
| Maximum included benefit share | 85% | IRS: Maximum taxable part | August 16, 2026 |
Additional procedural sources
Calculation method
The IRMAA engine selects the first published MAGI upper boundary that contains the entered amount, then adds the corresponding Part B and Part D adjustments to the standard Part B premium. The Roth comparison reports the Part B change, Part D IRMAA change, and combined annual change separately. The Social Security engine reproduces the common two-layer worksheet formula and caps included benefits at 85%.
Change log
| Date | Rule | Verification |
|---|---|---|
| August 16, 2026 | medicare-irmaa-2026 | Verified all individual, joint, and married-filing-separately tiers against the CMS fact sheet and exposed Part D IRMAA separately. |
| August 16, 2026 | social-security-benefit-inclusion-2025 | Verified the simplified combined-income thresholds and 85% cap against IRS Publication 915 for 2025 returns. |
Last reviewed August 16, 2026. Send corrections to [email protected].