Social Security and Medicare in 2026: Enrollment, Part B Costs, and IRMAA

Social Security and Medicare are separate federal programs — but the decisions you make in one can trigger consequences in the other. When you claim Social Security determines whether Medicare auto-enrolls you, how Part B premiums are deducted from your check, and whether a Medicare income surcharge shows up on your bill two years after a high-income year. This guide covers the rules most retirees learn too late, and the planning window where an advisor's coordination work pays off the most.

How Social Security triggers Medicare enrollment

If you are already receiving Social Security retirement or disability benefits when you turn 65, the SSA automatically enrolls you in Medicare Part A and Part B. No action is required. Your Medicare card arrives roughly three months before your 65th birthday, and Part B premiums are deducted directly from your Social Security check starting at enrollment.

If you have not yet claimed Social Security at 65 — for example, because you're delaying SS to 70 — Medicare will not enroll you automatically. You must actively sign up through SSA.gov or your local Social Security office. Many people who delay SS for the delayed credits don't realize they still need to act at 65 to avoid a late enrollment penalty.

Medicare enrollment windows

Initial Enrollment Period (IEP): 7 months around your 65th birthday

Your IEP runs for 7 months: the 3 months before your birthday month, your birthday month itself, and the 3 months after. If you enroll during the first 3 months, your Part B coverage starts the month you turn 65. Waiting until months 5–7 delays your coverage start by 1–3 months.

If you miss your IEP without a qualifying reason, you must wait for the General Enrollment Period (January 1 – March 31 each year), with coverage starting July 1. Every 12 months you went without Part B coverage during your IEP adds a permanent 10% late enrollment penalty to your Part B premium. At the current $202.90 base, each 12-month period of late enrollment adds about $20/month — permanently.

Special Enrollment Period (SEP): if you're still working at 65

If you are covered under a group health plan through your own active employment (or your spouse's active employment), you may delay Part B without penalty. The key word is active: retiree health plans, COBRA, and ACA marketplace coverage do not count as qualifying coverage for this purpose.

Once your employer coverage or employment ends (whichever comes first), you have an 8-month Special Enrollment Period to sign up for Part B without a late penalty. Don't assume COBRA buys you this window — it doesn't. The 8-month clock starts when active employment or employer coverage ends, regardless of whether you elect COBRA.

2026 Medicare Part B premium

The standard 2026 Part B monthly premium is $202.90 — up $17.90 from $185.00 in 2025.¹ The annual Part B deductible is $283. For most Medicare-eligible retirees already receiving Social Security, this premium is deducted from their monthly SS check.

The hold-harmless rule limits how much Part B premiums can rise in a given year for existing enrollees: the net dollar increase in your Part B premium cannot exceed the dollar amount of your Social Security COLA increase. In practice this means a small COLA year can constrain how aggressively CMS raises premiums for existing enrollees. However, IRMAA surcharges are not subject to hold-harmless protection — high-income retirees can see their Medicare cost jump regardless of their COLA amount.

IRMAA: the Medicare income surcharge

Higher-income Medicare beneficiaries pay more for Part B and Part D through the Income-Related Monthly Adjustment Amount (IRMAA). In 2026, IRMAA applies to individuals with modified adjusted gross income (MAGI) above $109,000 (single/HOH) or $218,000 (married filing jointly).²

IRMAA is calculated from your tax return two years prior. Your 2026 Medicare premium is based on your 2024 MAGI, which SSA receives from the IRS each fall. This 2-year lag creates both a trap and an opportunity: a high-income year in 2024 — a property sale, large Roth conversion, or business distribution — shows up in your 2026 Medicare cost even if your current income is much lower.

Appealing an IRMAA determination

If your income dropped significantly since the year used in your IRMAA determination — because you retired, sold a business, had a one-time distribution, divorced, or lost a spouse — you can request that SSA use a more recent year's income. File Form SSA-44 (Medicare Income-Related Monthly Adjustment Amount – Life-Changing Event).³ Qualifying events include:

• Marriage, divorce, or death of a spouse
• Work reduction or stoppage (including retirement)
• Loss of income-producing property (not from a voluntary sale)
• Loss or reduction of pension income
• Employer settlement payment received in the lookback year

If approved, SSA uses the income from your requested year, which can eliminate IRMAA entirely or reduce it to a lower bracket. Note: you'll need documentation — tax returns, a letter from your former employer, or a Social Security award letter.

How Social Security claiming age interacts with Medicare costs

Social Security benefits themselves are not directly included in MAGI for IRMAA purposes — but taxable Social Security (up to 85% of your benefit, depending on your provisional income) is. The cleaner way to think about it: MAGI for IRMAA is roughly your AGI plus tax-exempt interest. That includes taxable SS, pension income, IRA/401(k) withdrawals, wages, capital gains, and rental income.

This creates a critical planning window:

• Before you claim SS (the conversion window): If you retire at 62 but delay SS until 70, those 8 years have temporarily low income. This is your best opportunity for Roth conversions — you can fill lower tax brackets before SS income and Required Minimum Distributions stack up in your 70s. But each conversion also raises MAGI, so you need to watch IRMAA bracket thresholds as well as income tax brackets simultaneously.
• The RMD + SS double stack: When SS starts at 70 and RMDs begin at age 73 or 75 (SECURE 2.0⁴), income can spike sharply. If your pre-tax IRA balance is large, this stacking effect can push you into a higher IRMAA bracket permanently — raising your Medicare cost by $1,000–$5,800/year compared to the standard rate.
• The Roth conversion–IRMAA trap: A Roth conversion that makes tax sense can simultaneously push you over an IRMAA threshold. The $81.20/month surcharge at the first IRMAA tier (Tier 1 vs. standard) costs $974/year in extra Part B premiums. For a couple, that doubles to $1,948/year. Whether the Roth conversion is worth it depends on the after-tax math across both dimensions.

The Social Security claim-age calculator shows break-even and lifetime benefit by claiming age — but it doesn't model Medicare IRMAA. Optimizing all of these together — SS claiming date, Roth conversion amounts, IRA withdrawal sequencing, and IRMAA brackets — is exactly what a fee-only Social Security and retirement income advisor does.

If you have Medicare and employer coverage at the same time

Once enrolled in Medicare, coordination of benefits rules determine which plan pays first. If you work for an employer with 20 or more employees, your employer plan is primary and Medicare is secondary. For employers with fewer than 20 employees, Medicare is primary and your employer plan is secondary. Claiming Social Security does not change this — primary/secondary is determined by employer size, not your SS status.

If Medicare is secondary (larger employer), your employer plan pays first and Medicare picks up some or all of the remaining balance. If Medicare is primary (smaller employer), your employer plan may leave significant gaps, since it's designed to supplement a primary plan. Knowing which applies before you make coverage decisions at 65 can prevent large unexpected bills.

Sources

1. CMS — 2026 Medicare Parts A & B Premiums and Deductibles. Standard Part B premium $202.90/month (up from $185.00); annual Part B deductible $283; Part A inpatient deductible $1,736.
2. SSA POMS HI 01101.020 — IRMAA Sliding Scale Tables (December 2, 2025). Complete 2026 Part B and Part D IRMAA bracket tables by filing status, used verbatim in the lookup tool above.
3. SSA Form SSA-44 — Medicare Income-Related Monthly Adjustment Amount Life-Changing Event. Used to request use of more recent income year when IRMAA was set using a year with atypically high income.
4. IRS — Required Minimum Distributions (RMDs). SECURE 2.0 raised RMD starting age to 73 for those born 1951–1959 and to 75 for those born 1960 or later.
5. Medicare.gov — When Does Medicare Coverage Start?. Initial Enrollment Period timeline, Special Enrollment Period rules for employer coverage, and late enrollment penalty calculation.

IRMAA brackets verified against SSA POMS HI 01101.020 (updated December 2, 2025) and CMS 2026 Medicare Premiums fact sheet. Enrollment rules from Medicare.gov and SSA. Values verified as of April 2026.