Methodology

The survey

The American Housing Survey is sponsored by the U.S. Department of Housing and Urban Development and conducted by the U.S. Census Bureau every two years. It asks homeowners about the home improvement jobs of the two years before their interview: the kind of job, its cost, who did most of the work, the year and the main source of the money. One of its job categories is "Added or replaced septic tank".

We use the national public use files of the 2019, 2021 and 2023 surveys together. Data source and how to check our numbers

Why three surveys together

The 2023 survey has 149 septic tank jobs, too few to split by anything. The three surveys together have 471. Each survey asks about the two years before its interviews.

The surveys differ: in 2026 prices the median was $4,800 in the 2019 survey, $5,100 in the 2021 survey and $8,700 in the 2023 survey. The table by survey on the cost page shows each one. Every other figure reads the three together.

Which jobs are counted

• Owner-occupied homes. The survey asks only owners about home improvement jobs.
• Jobs with a cost above $0: 417 of the 471 records.
• Costs the owner reported. The public file marks every value the Census Bureau changed. When an owner did not give a cost, the Bureau filled one in from similar households. We leave those jobs out, and the jobs where the Bureau filled in who did the work. That leaves 331.
• Homes on a septic system at the time of the interview: 191 jobs done by a professional and 37 done by the household. Another 82 professional jobs are in homes on a public sewer; the survey does not say what they were, and they appear only in one table.

A job enters a group, such as a home size or a year built, only if the Census Bureau did not change that value for the home.

What a cost includes

The survey asks: "How much did the entire … job cost, including your costs and any amount covered by insurance, not counting your time?" A cost here is therefore the full cost of the job, including any part an insurer paid, without the household's own time. The Census Bureau rounds the costs in the public file and caps the very largest ones.

Median, middle half, low end and high end

• Median: half of the jobs cost less and half cost more.
• Middle half: the range from the 25th to the 75th percentile. One job in four cost less than the lower figure and one in four cost more than the upper figure.
• "1 in 10 cost less" and "1 in 10 cost more": the 10th and 90th percentiles.

Jobs are weighted with the household weight of their own survey. Percentiles are not interpolated: each one is the cost of one job. Calculated this way on the costs as reported, our figures match the Census Bureau's own verification table for 2023 in all 35 rows.

The 30-job rule

A figure is shown only for a group with at least 30 jobs. Thirty jobs still give only a rough figure, so every table and every calculator result shows its job count.

How the calculator combines your choices

The calculator reads its result from one group of real jobs. A group combines at most two of your choices.

• With one choice, the result is that group.
• With two choices, the result is the group that matches both, if it has at least 30 jobs. If it does not, the result uses one of the two and says so.
• If no group of at least 30 jobs matches, the result is the figure for all homes and says so. Nothing is modeled.

The quote check

The calculator places your quote among the jobs in the group you chose and reports the share that cost less. It works from the group's percentiles in steps of five, so the answer is worded with "about"; below the 5th or above the 95th percentile it is "lower than at least 95%" or "higher than at least 95%". A quote above the median is not necessarily too high: the survey does not record the size of the tank, the type of system or the soil.

Location

The public files identify Census regions and divisions, not states. When you pick a state, the calculator uses that state's region and says so. The Midwest has 27 jobs, fewer than 30, so a state there gets the figure for all homes.

Features of the home

These describe the home, not the job. Home size is the owner's estimate of the square footage of the whole home. For homes built before 2010 the file gives the decade in which the home was built. Water supply is the home's main source of water.

Years and today's prices

The jobs were done from 2017 to 2023. The figures are in 2026 prices: each reported cost is multiplied by a factor for the year of the job.

The index is the price index for residential improvements (home improvements) of the U.S. Bureau of Economic Analysis, the BEA (National Income and Product Accounts, Table 5.4.4, line 46; 2017 = 100). Its latest value is 158.793, for the second quarter of 2026; the factor for a year is that value divided by that year's average.

• It is not a new price survey. A figure in 2026 prices is what owners reported, carried forward by the change in the index.
• One index for every kind of home improvement. The price of septic work may have moved more or less than the index. Even in 2026 prices the 2023 survey lies above the two before it.
• Year, not month. The survey records the year of a job, so the average of that year is used.
• Rounding. Each cost in 2026 prices is rounded to the nearest $100; below $1,000 to the nearest $10, and below $100 to the nearest dollar.
• The reported costs stay visible. The table by survey on the cost page also gives the median as reported.
• Updates. The BEA publishes the index every quarter and revises earlier values. The figures here use its file released September 30, 2026.

Do-it-yourself jobs

A job counts as do-it-yourself when someone in the household did most of the work. Its cost leaves out the household's own time, so it is not comparable with a contractor's price. 84% of the jobs were done by a professional.

What the data cannot show

• The size of the tank, the type of system, the soil or the material.
• Whether a job was a tank alone, a tank with its drain field or a smaller replacement.
• States, counties or cities.
• The septic system of a newly built home.

The tank size calculator

The tank size calculator does not use the survey. Its numbers are the smallest septic tank each state's regulation allows for a home with one to six bedrooms, read from the state's own published text on October 8, 2026.

• A table by bedrooms (39 states): the number is the regulation's.
• A size from the daily flow (8 states): the regulation sets a flow per bedroom and a rule that turns the flow into a tank. The page shows the working.
• No state size (4): the page says who sets it and gives no number.
• Nothing is filled in. Where a state's table stops, the page gives the regulation's rule for larger homes in words.
• The smallest tank the rule allows. Several states ask for more with a garbage disposal or a pump; the page lists those rules.

The data source page gives each rule's number, its wording and the link.

Checking our work

Each time our data is built, the job counts, medians and means of the Census Bureau's verification table for 2023 are recalculated from the file first. If one row does not match, nothing is published. All 35 of 35 rows match; the data source page shows the row for septic tanks.