Every number on this site comes from a source we opened and read, listed on the page where it is used. The last full check was October 2026.
Cost ranges
- For each cost, we compare at least two published cost guides (for example Angi, HomeGuide, This Old House) and show their figures side by side in a "What the cost guides say" table.
- Our range spans what those guides report. Where they disagree a lot, as with mound systems, we say so and show both.
- Costs are for a typical US single-family home. Local prices can fall outside these ranges.
Calculators
- Tank size: we compare four real codes (the ICC model code, North Carolina, Washington and Pennsylvania) and recommend a size that meets all of them: 1,000 gallons up to 3 bedrooms, 1,250 for 4, then 250 more per bedroom. With a garbage disposal we add 50% as a safety margin; that margin is our own rule.
- Drain field: 120 gallons per bedroom per day (the design flow in North Carolina and South Carolina rules) divided by the middle of South Carolina's loading-rate range for the soil class.
- Pumping schedule: Oregon State University Extension's table of years between pumpings by tank size and household size, capped at 5 years, the top of the EPA's typical 3–5 year range.
- Installation cost: a range for the system type from the cost guides, plus perc test, permits and survey. The bedroom, area and site adjustments (about ±5–20%) are our planning assumptions, not published figures, and are labeled as such.
Your state and county rules always override these numbers. See the full source list.