Methodology · Data sources
How it works, and where our data comes from
BenefitDial is built on one simple rule: we use only public government files, and we show our math. Every number on this site traces back to a file that CMS, the Social Security Administration, or the Bureau of Labor Statistics publishes for anyone to download. We don't estimate in secret, and we don't add a thumb on the scale. This page walks through exactly how the calculations work — so a careful reader can check us.
Social Security
The COLA, step by step
Each year, Social Security benefits rise by a cost-of-living adjustment (COLA) so they keep pace with inflation. The percentage isn't a guess or a vote — it comes straight out of a formula written into law. Here is that formula in plain language.
The government tracks a specific inflation measure called CPI-W — the Consumer Price Index for Urban Wage Earners and Clerical Workers. It's a cousin of the more familiar CPI-U you hear about on the news, but the COLA law uses CPI-W, not CPI-U. The BLS publishes it every month as series CWUR0000SA0.
To set the COLA, Social Security looks at just one stretch of the year — the third quarter: July, August, and September. It averages the CPI-W for those three months, then compares that average to the same three-month average from the last year a COLA took effect. The percentage increase, rounded to the nearest tenth of a percent, is your COLA.
A worked example: the 2026 COLA
The 2026 COLA was exactly 2.8%, announced on October 24, 2025 (a few days later than usual because of the federal government shutdown). Here's how that number falls out of the two third-quarter averages:
| Step | Value |
|---|---|
| Average CPI-W, July–Aug–Sep 2024 (the base quarter) | 308.729 |
| Average CPI-W, July–Aug–Sep 2025 (the new quarter) | 317.373 |
| Increase: (317.373 − 308.729) ÷ 308.729 | 2.799…% |
| Rounded to the nearest tenth of a percent | 2.8% |
And here is how that 2.8% fits into recent history (the 2027 figure is an early estimate):
| Item | COLA |
|---|---|
| 2023 | 8.7% |
| 2024 | 3.2% |
| 2025 | 2.5% |
| 2026 | 2.8% |
| 2027 | 3.6% |
That's the whole calculation. No opinion, no adjustment — just two averages and a rounding rule. The 2027 COLA is an early estimate of 3.6% from The Senior Citizens League and AARP, and we label it that way everywhere it appears. The official 2027 figure arrives when the BLS releases September CPI-W and the SSA announces the COLA on October 14, 2026 at 8:30 a.m. ET.
From the raise to what lands in your account
The COLA raises your gross benefit, but Medicare Part B is usually withheld from your check. So the number that actually reaches your bank is: Net benefit = (your current benefit × (1 + COLA)) − your Medicare Part B premium. That's the exact formula behind our COLA calculator.
Medicare
How the Medicare plan data works
Every fall, CMS publishes a set of public files that spell out what happens to every Medicare Advantage and Part D plan for the coming year. Our "What Changed" tool is really just a careful reading of three of them, lined up side by side.
The Landscape file — this year's baseline
The Landscape files list which plans are offered in each county, along with the headline facts: monthly premium, deductible, and star rating. This is the snapshot of what's available and what it costs — the starting point for any comparison.
The Crosswalk file — the map from this year to next
The Crosswalk file is the one that makes a real year-over-year diff possible. It maps each plan's current ID to its ID for next year and flags what's happening to it — whether the plan is renewing, being consolidated into a successor plan, or terminating entirely. Without the Crosswalk you couldn't tell whether "your plan" next year is the same plan, a merged one, or gone. This file is what powers our comparison.
The Public Use Files and PBP — the fine print
The Part D formulary Public Use Files (PUFs) and the Plan Benefit Package (PBP) data hold the detail underneath the headline numbers: the specific benefits a plan covers and how it sorts drugs into pricing tiers. That's where the maximum out-of-pocket amounts and dropped extras in your comparison come from.
All of these files are public domain — released by CMS in late September or early October each year, and free for anyone to download. We don't get special access, and there's nothing proprietary about the data itself; the work is in reading it accurately and putting it in plain English.
Our data sources at a glance
| Source | What it powers | Format & cadence | License |
|---|---|---|---|
| CMS Landscape files | Plan availability by county, premium, deductible, star rating | Spreadsheet files, released late Sep / early Oct each year | Public domain |
| CMS Crosswalk files | Mapping of this year's plan IDs to next year's; renewal, consolidation, and termination flags — our year-over-year diff | Spreadsheet files, released late Sep / early Oct each year | Public domain |
| CMS Part D formulary PUFs | Covered drugs and pricing-tier detail | Public Use Files, released annually each fall | Public domain |
| CMS Plan Benefit Package (PBP) | Covered benefits, maximum out-of-pocket, extra benefits | Benefit data files, released annually each fall | Public domain |
BLS CPI-W (CWUR0000SA0) |
The inflation index behind the COLA calculation | Data series, published monthly | Public domain |
| SSA COLA announcement | The official cost-of-living adjustment percentage | Announcement, released once a year each October | Public domain |
An honest note about 2027
Until CMS publishes the official 2027 files (late September / early October), our plan tool runs on a structurally identical sample dataset — same fields, same layout, real behavior — so you can see exactly how the comparison works before the real numbers exist. The moment CMS posts the actual files, we load them and the tool becomes live. We would rather tell you this plainly than pretend the 2027 numbers are already final.
Staying current
How we keep it up to date
There's a clear rhythm to the benefits year, and we follow it. Each autumn, as the government posts new files, we ingest them:
- Late Sep – early Oct 2026 CMS releases the 2027 Landscape, Crosswalk, PUF, and PBP files. We load them, replacing the sample dataset, so the "What Changed" tool shows real plan changes.
- October 14, 2026 The BLS releases September CPI-W and the SSA announces the official 2027 COLA. We update the confirmed figure across the site.
- Each following October We repeat the same process every year: fresh CMS files, fresh SSA COLA, same public sources.
Future-year figures stay labeled as estimates until the official announcement lands. When the real number is published, the estimate is replaced — and the source is always one you can check yourself at CMS.gov, SSA.gov, and BLS.gov.
Frequently asked questions
Are you affiliated with Medicare, the SSA, or an insurance company?
No. BenefitDial is an independent utility. We use the same public government files anyone can download, but we're not affiliated with CMS, Medicare, the SSA, or any insurer. We are not a broker or agent: we take no carrier or broker commissions, we capture no personal information, we sell no leads or data, and we never recommend a specific plan for payment. We're supported only by programmatic display ads. To enroll, always use the official Medicare Plan Finder or call 1-800-MEDICARE.
Why CPI-W and not the CPI you usually hear about?
The COLA law specifically names CPI-W — the index for Urban Wage Earners and Clerical Workers. The more commonly quoted CPI-U (for all urban consumers) is a different series, and it isn't the one that sets your Social Security raise. We use CPI-W because that's what the law uses.
Can I check your numbers myself?
Do the tools store what I type?
No. The calculators run entirely in your web browser. We don't have a server that receives your benefit amount or your plan choice, and we never ask for your name, email, or phone number. See our privacy pledge.
See the data put to work.
Now that you know where every number comes from, try the two tools built on it.