Free Mortgage Calculator for St. Louis Home Buyers: Run the Numbers Before You Decide.
A monthly payment is more than principal and interest. Use this calculator to see how the home price, down payment, rate, term, taxes, insurance, and PMI all work together - so you walk into a conversation knowing what your budget really looks like.
“A calculator gives you a starting point, not a strategy. Once you see a number that feels right, that’s exactly when we should talk - so we can pressure-test it against your real goals and the loan options available to you.”
- Free to Use
- No Sign-Up Required
- Built by Greg Aftayev, NMLS #230559
- No Obligation
Or request a free assessment - no credit pull, no commitment
Your information is never sold or shared. We use it only to respond to your request.
Free Tool
What It Factors In
Greg Aftayev
NMLS #230559
A clear estimate of your full monthly payment - principal, interest, taxes, and insurance - in one place.
How to Use This Calculator
- Enter the home price and your planned down payment. The calculator defaults to a $400,000 home with $80,000 down (20% - no PMI).
- Set your interest rate based on a recent quote, or leave the default as a rough planning estimate.
- Choose a loan term - 30 years is most common. Try 15 years to see how your monthly payment and total interest change.
- Adjust property taxes and insurance to reflect your target county. St. Louis County runs approximately 1.2-1.4% annually; St. Charles County closer to 0.9-1.1%.
- Read the monthly breakdown - the education section below explains each component and what it means for your budget.
This calculator is provided by MortgageCalculator.org for general informational purposes only. Results are estimates and do not constitute a commitment to lend, a quote, or an offer of credit. Your actual rate, payment, and terms depend on a full review of your financial profile.
What Your Monthly Payment Actually Includes
A mortgage payment is made up of four components - principal, interest, taxes, and insurance (PITI). Greg Aftayev (NMLS #230559), a licensed mortgage loan originator in Missouri, Illinois, and Indiana with 28 years of active origination experience, finds that the component most buyers underestimate is not the mortgage itself, but the taxes and insurance collected alongside it every month.
Principal & Interest
The base repayment of your loan. Principal is the amount borrowed; interest is the lender's charge for providing it. On a $320,000 loan at 7% over 30 years, principal and interest total approximately $2,129 per month before taxes and insurance.
Property Taxes
Collected monthly in escrow and paid to the county annually. In the St. Louis metro, rates vary by county - St. Louis County typically runs 1.2-1.4% of assessed value; St. Charles County closer to 0.9-1.1% (per Missouri State Tax Commission assessor data). On a $400,000 home, that gap alone can mean $80-$200 per month in your escrow payment.
Homeowners Insurance
Lenders require coverage paid through monthly escrow. For most homes in the St. Louis area, expect $100-$200 per month depending on home value, age, construction type, and carrier.
Private Mortgage Insurance (PMI)
Required on conventional loans where the down payment is below 20% of the purchase price. PMI typically adds 0.5-1.5% of the loan amount annually - roughly $130-$400 per month on a $320,000 loan. Once you reach 20% equity, you can request removal.
30-Year vs. 15-Year: How Loan Term Changes the Math
The same loan amount at the same rate looks very different across term lengths. A 30-year term keeps monthly payments lower, but costs significantly more in total interest. A 15-year term raises the monthly payment - often by $600-$900 on a typical St. Louis purchase - but can save $100,000 or more in lifetime interest. Which makes sense depends on your income, other financial goals, and how long you plan to stay in the home.
| Loan Term | Monthly P&I | Total Interest Paid |
|---|---|---|
| 30-year at 7% | ~$2,129 | ~$446,500 |
| 15-year at 6.5% | ~$2,785 | ~$181,200 |
Based on a $320,000 loan (80% LTV on a $400,000 home). Rates are illustrative and do not constitute an offer or commitment to lend. Your actual rate depends on credit profile, loan type, lender, and market conditions at the time of application. Rate examples last reviewed June 2026.
How to Read What the Calculator Tells You
Once you have a monthly payment estimate, the next question is whether it fits within a healthy debt-to-income (DTI) ratio. Most conventional loan programs look for a front-end DTI - housing costs as a share of gross monthly income - below 28%, and a back-end DTI covering all monthly debt obligations below 43-45%.
As a practical example: a household earning $8,500 per month gross with $600 in existing monthly debt obligations has a back-end DTI ceiling of approximately $3,655 under the 43% limit. That leaves roughly $3,055 available for a total PITI payment - enough to support a purchase in the $350,000-$380,000 range depending on down payment and current rate.
If the calculator shows a number that feels like a stretch, that is useful information - not a dead end. A different loan program, a larger down payment, a different term, or a different purchase price may produce a payment that fits. This kind of scenario planning is what Greg works through with buyers before they begin house hunting across the St. Louis metro - including St. Louis County, St. Charles County, Jefferson County, and Franklin County.
If your number raises questions, schedule a free 15-minute call. Greg will review what the calculator shows, identify which loan programs apply to your situation, and give you an honest picture of what is realistic - no credit pull, no obligation.
What This Calculator Does Not Include
This tool covers the most common payment components - principal, interest, taxes, insurance, PMI, and HOA dues. It does not account for:
- FHA mortgage insurance premiums (MIP) - an upfront fee of 1.75% of the loan amount plus an annual premium of 0.55-1.05%, which significantly raises monthly costs on FHA loans
- Flood insurance - required for properties in FEMA flood zones, which are common in parts of St. Charles and Jefferson Counties
- Closing costs - typically 2-5% of the purchase price, paid at settlement and not reflected in the monthly payment
- Missouri first-time homebuyer program overlays - some programs modify payment structure in ways this calculator cannot reflect
If you are evaluating an FHA loan or a property in a flood zone, your actual monthly payment will be higher than this estimate. Greg can walk through the real numbers for your specific scenario.
Mortgage Calculator FAQ
Clear answers to what the numbers mean and how to use them.
Still have questions? Greg is happy to help.
Got a Number You Like? Let’s Make Sure It Holds Up.
A calculator can estimate a payment, but it can’t tell you which loan program fits your goals, how to structure your down payment, or where you might save. That is what a conversation with Greg is for.
Bring the numbers you ran here. In 15 minutes, Greg will tell you what’s realistic, what your options are, and the smartest next step - free and with no obligation.
Not ready to call? Leave your details and Greg will reach out.
Your information is never sold or shared. We use it only to respond to your request.
Your Strategy Call
From Estimate to Action Plan
Greg reviews your numbers, your goals, and your options - and gives you an honest next step.
Greg Aftayev
Owner, Homestead Financial Mortgage