Septic system cost for a new conventional install is $6,000 to $15,000 in most yards, and $10,000 to $35,000 once the soil needs a pump, an aerobic unit or a mound. A single national average is a bad way to budget, because the tank is a known product and the field is a hole in your specific dirt. Set bedrooms, soil and system type above. The tool prices the same six line items every installer bids, then scales the tank and the field with the size the calculator on the homepage just produced.
What drives the price of a septic system
Four things, in this order: the soil, the system type the soil forces, access for the trucks, and only then the tank. Two three-bedroom houses a mile apart can be $8,000 apart on the bid for no reason other than minutes per inch and whether an excavator can reach the back yard.
| Line item | Low | High |
|---|---|---|
| Permit and perc test | $400 | $2,000 |
| Site evaluation and design | $350 | $1,800 |
| Tank supplied and set | $1,200 | $3,600 |
| Excavation and backfill | $1,500 | $6,000 |
| Drainfield materials and labor | $2,200 | $9,500 |
| Connection to the house | $500 | $2,500 |
Add the lows and you are near $6,150. Add the highs and you are past $25,000. That is why the typical conventional job is quoted as $6,000 to $15,000: most yards are not the worst case on every line at once. Tank cost grows slowly above 1,000 gallons, about $0.55 to $1.35 per extra gallon. Field cost grows with area, about $2.40 to $8.50 per extra square foot above a 600 square foot baseline. Slow soil is what inflates the bill.
Cost by system type
| Type | Typical | Range |
|---|---|---|
| Conventional gravity | $9,000 to $12,000 | $6,000 to $15,000 |
| Chamber | $10,000 to $13,000 | $6,500 to $16,000 |
| Pressure dosed | $12,000 to $16,000 | $9,000 to $20,000 |
| Aerobic (ATU) | $16,000 to $22,000 | $10,000 to $25,000 |
| Mound | $22,000 to $28,000 | $15,000 to $35,000 |
Conventional gravity is the cheapest to own as well as to install: no power, no service contract, pump the tank every few years. Every other type exists because a perc test, a water table or a tight lot ruled conventional out. Choosing an aerobic unit on soil that would have taken a gravity field buys a $400 to $900 yearly bill you did not need. The types page is when each one is actually required.
3 bedroom and 4 bedroom septic system cost
A three bedroom house on loam is the reference case: a 1,000 gallon tank and about 600 square feet of field, commonly $8,000 to $13,000 on a reachable lot. A four bedroom house steps the tank to 1,250 gallons and adds a little trench. That is usually $800 to $2,500 more, not a different job. Five bedrooms step the tank to 1,500. Soil moves the price more than an extra bedroom does. The same three bedroom house on silty clay can cost as much as a five bedroom house on sand.
- 3 bedroom, sandy loam: often $6,500 to $11,000.
- 3 bedroom, loam: $8,000 to $13,000.
- 3 bedroom, clay loam or worse: $11,000 to $18,000, or a jump to an alternative system.
- 4 bedroom on good soil: add $800 to $2,500 to the three bedroom figure.
How much does a septic tank cost, on its own?
The tank, supplied and set, is $1,200 to $3,600 for a 1,000 gallon concrete unit, more as capacity goes up. That is the number people mean by "how much does a septic tank cost," and it is the smaller half of the system. Replacing only a cracked or rusted tank, hooked to a field that still works, is commonly $3,000 to $8,000 including the connection. Replacing only the field is $5,000 to $20,000 and is the more common half-job. If both are shot, price them as one mobilization.
A failed field often has to be dug out, not just replaced beside the old one, and the county will size you to today's code, not the 1985 permit. That is why "cost of septic tank replacement" and "new system cost" overlap and still come out different. The drain field replacement page is the failed-field version of this calculator.
What a quote should show you
- Permit, design and perc as their own lines, or a clear note that you are paying them yourself.
- Tank size in gallons, not "standard tank." Ask which rule set the gallons: bedrooms, retention or a state minimum.
- Field area in square feet and the perc rate it was designed against.
- System type, in the words the county uses.
- Restoration. Seed and grade, or "site left as is." Mature landscaping does not come back.
- What happens if they hit rock or water. That is the change-order that blows a low bid up.
How to use the calculator above
It is the same engine as the septic tank size calculator: bedrooms, occupants, perc and system type in, gallons and square feet through the middle, dollars out. Change the soil band and watch the field line move. Change the system type and watch the multipliers. The range is wide on purpose. A real bid will land inside it; a bid well under the low end is usually missing the permit, the design or the restoration. The tank and leach field cost page is the same package in prose if you want to read it before you set the sliders.