New construction mortgage calculator
Estimate the monthly payment on a new home in St. Clair or Monroe County, IL, with principal, interest, property tax, insurance, HOA and PMI. Every default has a source below.
Monthly payment estimate
Prefilled: an example price of $400,000, so enter the home you are looking at. Change any number.
County average: St. Clair 2.63%, Monroe 1.99% (IL Dept of Revenue, 2024).
Illinois average (NAIC, 2023 data).
None listed by the builders; ask before you sign.
Example, ask your lender; typical range 0.19% to 1.86% per year, Urban Institute 2021. Applies only with less than 20% down.
Rate: Freddie Mac 30-year average 7.32%, week of Oct 22, 2026 (Freddie Mac PMMS); 15-year 6.68%. Property tax: county average residential tax rate, 2024 (St. Clair 7.88, Monroe 5.96 per $100 of assessed value; Illinois assesses homes at one third of market value, so about 2.63% and 1.99% a year before the homestead exemption) (Illinois Department of Revenue, Table 08). Your rate depends on the school district, township and city. Insurance $1,480 a year, the Illinois average (NAIC, 2023 data). Estimate only, not a loan offer. Taxes, insurance and rates vary.
Common questions
What interest rate does the calculator start with?
The Freddie Mac 30-year average, 7.32% for the week of Oct 22, 2026. Your rate depends on credit, down payment and the lender. Some builders offer a lower rate through their own lender; compare Loan Estimates side by side.
What property tax rate does it use?
The county average residential tax rate for 2024 from the Illinois Department of Revenue: 7.88 per $100 of assessed value in St. Clair County and 5.96 in Monroe County. Illinois assesses homes at one third of market value, so that is about 2.63% and 1.99% of the price a year before exemptions. The real rate depends on the school district, township and city, and the homestead exemption lowers it for an owner-occupied home.
Why can the tax bill be lower in the first year?
A new home is often taxed on the lot only until the house is assessed, so the payment can rise in year two. Budget for the full amount.
What insurance cost does it use?
$1,480 a year, the Illinois average homeowners (HO-3) premium in the NAIC report for 2023. Premiums have risen since, so get a quote.
Do I need PMI?
Only with less than 20% down on a conventional loan. The calculator uses 0.50% a year of the loan as an example; the typical range is 0.19% to 1.86% (Urban Institute, 2021). Your lender quotes the real number.
Get the builder offers for St. Clair and Monroe County
Craig will email you the current builder offers and prices for the 20 communities on this page, or send new homes as they list.
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Thinking about building?
The builder's sales agent works for the builder. Craig Ziegel can represent you: compare builders and lots, review the contract and walk-throughs.
Call or text 618-719-4543.
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