This free PFAS hazard index calculator checks your drinking water PFAS results against EPA limits in one step. Enter the PFAS results from your water test in parts per trillion (ng/L). The calculator compares each one with the EPA drinking water standards, calculates the Hazard Index for PFAS mixtures, and explains what is enforceable right now given the EPA’s 2026 proposals.
Leave a result at 0 if it was not detected (“ND” or “< MRL”).
How to use the PFAS Hazard Index Calculator
- Pick the result unit used on your report (ppt/ng/L or ppb/µg/L).
- Enter PFOA, PFOS, PFHxS, PFNA, HFPO-DA (GenX) and PFBS. Leave untested compounds blank.
- Press Check my PFAS result.
- Compare each result with its limit and read the Hazard Index for the mixture.
If any result is at or above a limit, share the PFAS hazard index calculator output with your water supplier or a certified lab. For the latest rule status, see EPA’s PFAS drinking water page.
EPA PFAS drinking water limits (2026 status)
| PFAS | 2024 EPA MCL | Status as of 2026 |
|---|---|---|
| PFOA | 4.0 ppt | In force. Compliance proposed to move from 2029 to 2031 |
| PFOS | 4.0 ppt | In force. Compliance proposed to move from 2029 to 2031 |
| PFHxS | 10 ppt | Proposed for rescission (May 2026) |
| PFNA | 10 ppt | Proposed for rescission (May 2026) |
| HFPO-DA (GenX) | 10 ppt | Proposed for rescission (May 2026) |
| Mixture Hazard Index (PFHxS, PFNA, GenX, PFBS) | 1.0 (unitless) | Proposed for rescission (May 2026) |
The EPA’s health goal (MCLG) for PFOA and PFOS is zero. Rules can change after the public-comment process and any litigation, so check the EPA PFAS page and your state’s standards for the latest position.
How the Hazard Index works
Each compound is divided by its health-based water concentration, so the HI adds up the fraction of the “safe” level used by each chemical. This accounts for combined exposure even when every individual PFAS is below its own limit.
Who should test for PFAS?
- Private well owners within a few miles of airports, military bases, fire training areas, landfills, wastewater plants, or plating, textile and paper industries.
- Homes where biosolids (sewage sludge) were spread on nearby farmland.
- Anyone on a public system that has reported PFAS in its Consumer Confidence Report.
Use a laboratory accredited for EPA Method 533 or 537.1 and follow its sampling instructions exactly. PFAS are in many everyday materials, so contamination during sampling is a real risk.
Frequently asked questions
What is a safe level of PFAS in drinking water?
The EPA’s enforceable limit is 4 parts per trillion each for PFOA and PFOS, and its health goal for both is zero. For PFHxS, PFNA and GenX the 2024 limit is 10 ppt, but the EPA proposed removing those limits in 2026.
How do I convert ppb to ppt?
1 ppb (µg/L) = 1,000 ppt (ng/L). Select “ppb” and the calculator converts automatically.
Does boiling water remove PFAS?
No. Boiling does not remove PFAS and can slightly concentrate them. Use reverse osmosis or a filter certified for PFOA/PFOS reduction.
Are the EPA PFAS limits still in effect?
The PFOA and PFOS limits of 4 ppt remain. In May 2026 the EPA proposed rescinding the limits for PFHxS, PFNA, GenX and the Hazard Index, and extending the PFOA/PFOS compliance date to 2031. Those proposals were not final at the time of writing.
How do you calculate the hazard index?
Divide each result by its health-based water concentration and add the ratios: HI = GenX/10 + PFBS/2000 + PFNA/10 + PFHxS/10 (all in ppt). A total above 1.0 exceeds the Hazard Index. For example, PFHxS at 6 ppt and PFNA at 5 ppt give 0.6 + 0.5 = 1.1.
What are the PFAS MCLs?
EPA’s 2024 rule set MCLs of 4.0 ppt each for PFOA and PFOS, 10 ppt each for PFHxS, PFNA and HFPO-DA (GenX), and a Hazard Index of 1.0 for mixtures of PFHxS, PFNA, GenX and PFBS. EPA has since announced changes to parts of the rule and later compliance dates, so check the current status on EPA’s site.
Related tools
General information only, based on US EPA drinking water rules as published through mid-2026. Not medical advice. Check your state’s standards and speak to your laboratory or a certified water treatment professional. Built by an accredited water-testing laboratory professional.