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Mitigating 6→2 pCi/L removes 16.5 per 1,000 of lung-cancer risk for a smoker — $73 per point. For a never-smoker the same system is $643 per point. Radon math is smoking math.
Radon is the #2 cause of lung cancer in the US and the #1 cause among never-smokers — an odorless soil gas entering through slab cracks, fixable for $800–1,500 with sub-slab depressurization. Whether it pencils depends on arithmetic most contractors skip: EPA lifetime risk at the 4 pCi/L action level is ~7 per 1,000 for never-smokers but ~62 per 1,000 for smokers — the same mitigation from 6 to 2 pCi/L removes 16.5 per 1,000 of risk for a smoker (about $73 per point at $1,200) versus 1.9 per 1,000 for a never-smoker ($643 per point). This calculator prices your level, your years in the home, and your smoking status honestly — plus the resale reality that radon above 4 surfaces on every inspection.
Homeowners use it after a radon test: mitigating 6→2 pCi/L removes 16.5 per 1,000 of lung-cancer risk for a smoker ($73 per point) versus 1.9 for a never-smoker ($643 per point) — radon math is smoking math.
Cheaply and carefully, because test conditions change the number. A $15–25 charcoal short-term kit from any hardware store, placed in the lowest lived-in level of the home (the basement you use, or the first floor if the basement is storage), for 48–96 hours with windows and exterior doors closed except normal entry — the closed-house condition matters because ventilation dilutes the reading. Test in winter if you can: the stack effect (warm house pulling soil gas upward) peaks in heating season, giving the conservative number. Avoid testing in storms or high wind, which skew results. If the short-term test reads 4–10, confirm with a long-term alpha-track kit (90+ days, $25–30) before spending $1,200 — radon fluctuates seasonally and a single short test can over- or under-read. Readings above 10 justify faster action: a pro continuous-monitor test ($150) and a mitigation quote in parallel. And retest after mitigation — the installer should guarantee a post-mitigation number in writing.
Sub-slab depressurization, and it is less invasive than it sounds: a 4-inch PVC pipe core-drilled through the slab (or into the sump pit), run to an inline fan, and vented above the roofline — the fan creates negative pressure under the slab so soil gas goes up the pipe instead of into the house. One day of work, $800–1,500 in most markets (higher for large footprints, crawlspace encapsulation add-ons, or finished basements where pipe routing is harder), and typically a 50–99% reduction in levels. Operating cost is trivial — the fan draws 40–90 watts, roughly $50–110/yr of electricity. Maintenance: check the manometer (the little U-tube gauge) occasionally to confirm the fan runs; fans last 10–15 years and cost $150–250 to replace. What NOT to do: sealing cracks alone does not fix radon (the house just pulls harder elsewhere), and ventilation-only approaches work inconsistently. Get 2–3 quotes from certified mitigators (state radon offices maintain lists) — the technique is standardized enough that price shopping is legitimate.
The honest answer is that 4 is a policy line, not a safety cliff — EPA itself says consider fixing between 2 and 4, and WHO recommends action at 2.7. The risk is roughly linear, so 4 pCi/L is not twice as dangerous as 2; it is twice the risk, period, with no threshold where it becomes zero. That makes the below-4 decision personal: this calculator exists for exactly that call. The inputs that argue for mitigating below 4: smokers or former smokers in the house (the multiplier), children (long exposure runway), a basement used as living space (levels are usually highest there), and a long ownership horizon. The inputs that argue against: never-smokers, a rarely-used basement, and a level barely above 2. The resale wildcard: buyers increasingly test, and while 4 is the negotiation trigger, a documented low number with an installed system is a listing asset. At $800–1,200 against decades of exposure, many families treat it as cheap insurance — that is a legitimate use of expected-value math with anxiety priced in.