One month is in. Two are not.

Right now a number is being written that decides how much Social Security adds to benefits this December, which is the payment that reaches you in January. Nobody is voting on it. It is arithmetic, it is already partly finished, and one third of it is published where anyone can read it.

You may also have seen a video promising that this could be the biggest raise ever recorded. So here is what actually exists on the first days of September 2026, what doesn't exist yet, and the deduction that comes out of the payment before any of it reaches your bank.

What was the biggest Social Security raise ever?

There are two answers, and the difference is the whole subject. The largest automatic cost-of-living adjustment was 14.3%, for 1980.Source: SSA, Cost-of-Living Adjustments.

There was a bigger increase than that: 20%, effective September 1972. Congress voted it. The same 1972 amendments then created the automatic mechanism, so that nobody would have to vote on it again. Every adjustment since has come out of that formula, not out of a debate.Source: SSA, Social Security Amendments of 1972.

The one month of 2027's calculation that is public sits nowhere near either figure. That is the honest starting point, and the rest of this page is about how much of the answer you can see today.

How is the Social Security COLA actually calculated?

The rule is written into the Social Security Act, and SSA states it in one paragraph on its determination page.

Three inputs, one subtraction, one rounding step. Every number in this article comes from SSA's own pages and tables, the 2026 Medicare premium from a CMS fact sheet, and the 2027 estimates from the Medicare Trustees Report. The links are beside each figure.

What is already locked?

The first half of the comparison is finished and can't move. The base is the third-quarter average from 2025: July at 316.349, August at 317.306, September at 318.139. Average those three and you get 317.265.Source: SSA, Latest Cost-of-Living Adjustment, computation table.

Nothing that happens between now and October changes that number. It is the base that 2026's third-quarter average gets measured against, and it is the same base that produced the 2.8% adjustment paid from January 2026.

How much of the 2027 calculation is public today?

One month of three. July 2026 is published: CPI-W came in at 327.104. August and September are empty cells in SSA's table.Source: SSA, CPI-W monthly table, 2026 row, read 1 September 2026.

Hold July against the 317.265 base and that single month stands 3.1% higher. The arithmetic is (327.104 − 317.265) ÷ 317.265, which is 3.101%, rounded to the nearest tenth.

This is exactly where the internet stops being honest. When somebody hands you a firm figure for next year right now, they aren't reading the determination. They are handing you a forecast wearing the clothes of a rule. And withholding the official estimate while complaining about other people guessing would be the same trick in the other direction, which is why the 2.7% is on this page with its source.

So there is a test you can use on anything you are shown between now and October. Ask one question: is this an estimate, or was it calculated from all three published months? Today, all three haven't been published, so every firm figure in circulation is the first thing and not the second.

Where does that sit against the record?

Recent adjustments, by the year they were determined: 5.9% for 2021, 8.7% for 2022, 3.2% for 2023, 2.5% for 2024 and 2.8% for 2025.Source: SSA, Cost-of-Living Adjustments.

The 1980 record came out of an inflation era nobody wants back. That is the thing about a large adjustment: it isn't a gift. It reflects a rise in the price basket the index tracks, which may not match what your own month actually costs you.

Can the COLA be zero?

Yes, and it has been. The rule says plainly that if there is no increase, or the rounded increase comes out to zero, there is no adjustment that year. SSA's published series shows three zero determinations: 2009, 2010 and 2015. The one that followed the 2015 zero was 0.3%, for 2016.Source: SSA, Cost-of-Living Adjustments.

That is the clearest proof that this is a calculation and not a decision somebody makes on your behalf. When the third-quarter average didn't rise far enough above the base still in force, the formula produced zero, and no one could vote it higher.

Who does the adjustment reach?

It applies to Social Security benefit computations and to federal Supplemental Security Income payment levels. For scale, take the one that already happened. The 2.8% adjustment reached 75 million Americans: benefits payable to nearly 71 million Social Security beneficiaries in January 2026, and increased payments to nearly 7.5 million SSI recipients beginning December 31, 2025. The groups overlap, which is why they add up to more than 75 million: some people receive both.Source: SSA, COLA Information for 2026.

Federal SSI payment levels get the same percentage, while what an individual actually receives depends on countable income and on any state supplement, which runs under its own rules. Retirement, survivors and disability benefits all sit inside the same computation. If you are still deciding when to start, when to claim is the decision that dwarfs any single year's adjustment.

What comes out before the raise reaches you?

For most people on Medicare, the Part B premium is deducted from the Social Security payment before it reaches the bank. That premium moves on its own schedule, for its own reasons, in its own announcement.

So the premium can eat into your raise. For most people it can't eat more than the raise. Your own deduction can still differ: an income-related surcharge or a late-enrollment penalty changes what you are charged, and an assistance program may pay some or all of it for you. The premium itself may also be deductible on your return, which is a separate question with its own hurdles.

Why do two people with the same percentage see different checks?

Because the percentage is applied to an underlying figure, not to the deposit. SSA says a COLA raises a retirement benefit by approximately the product of the COLA and the benefit amount, and that the exact computation is more complex. The adjustment is applied to your primary insurance amount and truncated to the next lower dime. Then the factors and offsets that belong to your record are applied, and the amount actually payable is truncated to the next lower dollar.Source: SSA, Application of COLA to a Retirement Benefit.

What lands in your account is that recalculated benefit after Part B and any other deduction on your record. Two people get the identical percentage and can still see different dollar changes. Whether the raise is then taxed is one more step that depends on the rest of your income, not on the adjustment.

How do you check any number you are shown?

Without taking anyone's word for it, including ours. SSA publishes the determination on its own actuarial pages, and the whole audit takes two minutes.

You don't need to be good at arithmetic to do this. You need to check whether the months they are counting on have been published yet. One footnote on that table matters too: BLS didn't publish an October 2025 index at all, because a lapse in appropriations stopped the survey and the data couldn't be collected afterwards. Published months aren't guaranteed.Source: SSA, CPI-W monthly table, footnote a.

When is the number real, and what should you do until then?

The third month in the calculation is September, and September's index is normally scheduled to publish the following month. Nobody outside those agencies can calculate the official figure from published data before then. Any number you see before that is somebody's model.

When it does land, it doesn't reach you that month. For Social Security it takes effect with December's benefits, and December's benefit is the payment that arrives in January. SSI runs on its own timing, and because January 1 is a holiday the January SSI payment is made at the end of December. That gap is normal, and it catches people out every single year.Source: SSA, Latest Cost-of-Living Adjustment.

The honest verdict

The record for an automatic adjustment is 14.3%, from 1980. The formula for next year is fixed in law, the base is locked at 317.265, and July 2026 is the one month that is public, standing 3.1% above that base. SSA's actuaries estimate 2.7%. August and September will decide the rest, and until they publish, nobody has the number. Not the channels promising you one, and not us.

If the longer horizon is what worries you, the 2032 trust fund question is the one that actually changes the arithmetic, and it is a different rule from this one.

Check the rule. Not the slogan.

What to check this week

• Pull up your my Social Security account and read your current monthly benefit amount, the actual figure, not the one you remember. Multiplying it by any percentage gives a rough estimate and only that.
• Check whether Part B is being deducted from your payment. If it is, your net change depends on the recalculated benefit, on hold harmless if it applies to you, and on every other deduction on your record.
• Wait for the notice SSA sends with your recalculated benefit. That number counts. The subtraction in your head does not.
• Do not make a decision about claiming, working, or moving money on a predicted adjustment. It is one third measured and two thirds unwritten.
• Run the two-page check on any figure you are shown before October.

Educational only

This is general information, and it isn't legal, tax or financial advice. Benefit amounts and premiums depend on your own record and your own coverage, and only Social Security and Medicare can apply a figure to your situation. The 2026 amounts above change every year. Confirm anything that matters at ssa.gov or by calling Social Security directly.

Sources

• SSA: Latest Cost-of-Living Adjustment (the formula, the rounding rule, the zero rule, the 317.265 base and its three months, the December/January timing)
• SSA: CPI-W monthly table (July 2026 at 327.104, August and September unpublished, the October 2025 footnote)
• SSA: Estimates under the 2026 Trustees Report (the 2.7% actuarial estimate)
• SSA: Cost-of-Living Adjustments (14.3% for 1980, the recent series, the three zero years)
• SSA: Social Security Amendments of 1972 (the 20% legislated increase and the creation of the automatic mechanism)
• SSA: COLA Information for 2026 (75 million, 71 million, 7.5 million)
• SSA: Application of COLA to a Retirement Benefit (PIA, truncation to the dime and to the dollar)
• CMS: 2026 Medicare Parts A & B Premiums and Deductibles ($202.90, $185.00, $283)
• CMS: 2026 Medicare Trustees Report (the $209.50 estimate, the hold-harmless provision)

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