The cost to install a septic tank and leach field as one job is $6,000 to $15,000 for a conventional gravity system on workable soil, and $10,000 to $35,000 once the site needs a pump, an aerobic unit or a mound. People search the two pieces together because that is how the bid arrives: one crew, one permit, one hole in the yard. The tank is the smaller line. The leach field, the excavation and the soil test are where the quotes spread out.
The package price, 2026
| System | Typical package | Range |
|---|---|---|
| Conventional gravity | $9,000 to $12,000 | $6,000 to $15,000 |
| Chamber leach field | $10,000 to $13,000 | $6,500 to $16,000 |
| Pressure dosed | $12,000 to $16,000 | $9,000 to $20,000 |
| Aerobic (ATU) plus field | $16,000 to $22,000 | $10,000 to $25,000 |
| Mound | $22,000 to $28,000 | $15,000 to $35,000 |
Those ranges assume a three or four bedroom house, a reachable back yard and a perc test that allows a conventional or near-conventional field. A rocky slope, a well inside the setback or a reserve area that was built on will not land in the typical column. The septic system cost calculator prices the same job from your bedrooms, soil and system type, line by line.
Where the money goes
| 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 those lows and you are near $6,150. Add the highs and you are past $25,000, which is why a single national number is a bad way to budget. On a friendly sandy lot the field and the digging stay near the bottom. On clay, or on a lot that needs a mound of imported sand, those two lines dominate. Tank cost scales slowly with gallons (roughly $0.55 to $1.35 per gallon above 1,000). Field cost scales with area, at roughly $2.40 to $8.50 per extra square foot above a 600 square foot baseline.
Septic tank and leach field cost by house size
Bedroom count sets the tank and the design flow, which sets the field. A three bedroom house on loam (about 16 to 30 minutes per inch) is the reference case most quotes are built around: a 1,000 gallon tank and a field on the order of 600 square feet of trench bottom. Four bedrooms steps the tank to 1,250 gallons. Five bedrooms steps it to 1,500. Slow soil grows the field much faster than extra bedrooms grow the tank, which is why two houses with the same bedroom count can be thousands apart.
- 3 bedroom, sandy loam: often $6,500 to $11,000 for tank and field together.
- 3 bedroom, loam: $8,000 to $13,000.
- 3 bedroom, clay loam or silty clay: $11,000 to $18,000, or a jump to an alternative system.
- 4 or 5 bedroom on good soil: add $800 to $2,500 for the larger tank and the extra trench.
If one quote says leach field and another says drain field, they are pricing the same trenches. Regional habit, same work. The drain field page unpacks the layout. What changes the price is soil and access, not the noun.
What is not in the package price
- A well that has to move because it sits inside the new setback.
- Tree clearing, fence work and a driveway the trucks will ruin.
- Landscaping that was on top of the old field. Restoration is usually seed and hope.
- A pump and panel if the field is uphill of the tank. That is a $2,000 to $5,000 add.
- Indoor plumbing changes if the house drain is in the wrong place.
What makes two bids $8,000 apart
- The perc test. Slow soil means more trench, or a different system. Do this first. See what a perc test costs.
- Access. If the excavator cannot reach the back yard, someone is taking a fence down and building a path.
- Rock or a high water table. Either one can turn a conventional field into a mound.
- Haul distance for gravel or sand. The material is cheap at the pit and expensive on your road.
- Who is pulling the permit. Some installers include design and county fees. Some do not.
Tank-only or field-only jobs
Replacing just the tank, because it cracked or it is an old steel tank, is commonly $3,000 to $8,000 including the hookup to an existing field that still works. Replacing just the field, because the soil sealed, is $5,000 to $20,000 and is the more common half-job. If both are shot, price them as one mobilization. Two separate crews two years apart costs more than one permit and one excavation.