Most online mortgage calculators get the payment math right and the local cost layer wrong. They show you principal and interest plus a generic property-tax estimate and call it a day. In Simi Valley and the rest of Ventura County, the real monthly carrying cost includes property tax (1.10-1.25% effective), HOA dues in master-planned communities, Mello-Roos (CFD) assessments in Wood Ranch, Big Sky, Sycamore Grove, and newer Moorpark or Camarillo tracts ranging from $1,500 to $5,500 per year, and hazard insurance that has moved meaningfully higher post-Woolsey. The calculator on this page handles all of it. Enter your numbers and see the full monthly cost — not just P&I.
Use the calculator
Enter your numbers below. The calculator runs entirely in your browser — nothing is saved or transmitted. Final numbers come from your lender's Loan Estimate (within three business days of application) and the Closing Disclosure (three business days before signing). Confirm with your lender, escrow officer, and insurance broker before relying on the result.
Estimate only. Confirm rate, taxes, HOA, Mello-Roos, and insurance with your lender and escrow officer before relying on the result.
What the calculator includes (and what it doesn't)
Includes: principal and interest computed via the standard amortization formula, property tax estimated as a percent of purchase price (default 1.15% which is reasonable for Ventura County including voter bonds), Mello-Roos (CFD) as an annual figure converted to monthly, hazard insurance as an annual figure converted to monthly, and HOA dues as a monthly figure.
Does not include: PMI (private mortgage insurance) for down payments under 20%, FHA MIP, VA funding fee, jumbo overlays, or any temporary buydown amortization. For PMI scenarios, add roughly 0.3-0.8% of loan amount divided by 12 to the monthly. For FHA, add the upfront 1.75% to the loan and the annual MIP based on the LTV table. For VA, the funding fee is typically rolled into the loan rather than paid monthly.
Also does not include flood insurance (required only in FEMA Special Flood Hazard Areas — Simi Valley has limited SFHA exposure but parts along the Arroyo Simi corridor do require it), earthquake insurance (separate California Earthquake Authority policy, typically $1,200-$3,500/year for a Simi Valley home), or umbrella liability.
The math behind P&I
Principal and interest is computed via the standard fixed-rate amortization formula. For a loan amount L, monthly rate r (annual rate divided by 12), and total payments n (term in years times 12), monthly P&I is L * r * (1+r)^n / ((1+r)^n - 1).
Worked example: $885,000 home, 20% down, 6.75% rate, 30 year term. Loan amount $708,000. Monthly rate 0.005625. Total payments 360. Monthly P&I = $708,000 * 0.005625 * (1.005625)^360 / ((1.005625)^360 - 1) = $4,592.
The same loan at 6.0% rate would be $4,246/month — a $346 difference. At 7.5% it would be $4,950 — a $358 difference the other way. Rate sensitivity at this loan size is roughly $50/month per 0.125% rate change.
Property tax in Ventura County
California Prop 13 sets the base rate at 1% of assessed value. Voter-approved bonds for schools, water, and other local infrastructure add typically 0.10-0.25% on top, producing an effective rate of 1.10-1.25% in most Ventura County jurisdictions.
Simi Valley's effective rate including voter bonds runs about 1.13-1.18% in most TRA (Tax Rate Areas). Use 1.15% as a planning default. For exact rate, look up the parcel on the Ventura County Assessor portal — the secured tax bill shows the precise rate for the parcel's TRA.
Important: at purchase, your assessed value resets to the purchase price under Prop 13. So if you buy for $885K, your initial property tax base is $885K (not the prior owner's assessed value). The listing-sheet 'taxes' field often reflects the prior owner's basis and will under-state your actual first-year bill significantly.
Mello-Roos (CFD) — the line item that surprises buyers
Mello-Roos refers to Community Facilities Districts (CFDs) created under the 1982 Mello-Roos Community Facilities Act. CFDs fund infrastructure (schools, roads, parks) in master-planned communities through a special tax that runs with the property, typically for 25-40 years from initial issuance.
Simi Valley CFD-affected neighborhoods include Wood Ranch ($1,500-$3,500/year typical), Big Sky ($2,500-$5,500/year typical), and parts of Sycamore Grove ($1,800-$3,200/year typical). Most older Simi neighborhoods (Texas Tract, Indian Hills, Sequoia area, original Mountain Gate sections) have no Mello-Roos.
Verify the actual CFD assessment by looking up the parcel on the Ventura County Assessor secured tax bill. The bill itemizes the base 1% tax, voter bond add-ons, and any CFD assessments separately. Listing-sheet 'taxes' figures often quote only the base rate and miss the CFD — always pull the actual tax bill before contingency removal.
Homeowners insurance in Simi Valley post-Woolsey
Insurance is the cost line that has changed most in the past several years. Pre-Woolsey (2018), a Simi Valley home outside the highest fire zones typically insured for $1,200-$1,800/year baseline. In 2026, that range has roughly doubled — baseline policies commonly run $2,000-$3,200/year, with hillside and wildland-urban-interface properties running $4,500-$10,000+/year.
The calculator default of $2,400/year is reasonable for a mid-Simi-Valley home outside the highest fire zones. For Wood Ranch, Big Sky, Long Canyon, and the hillside edges in CAL FIRE Very High Fire Hazard Severity Zones, use $5,000-$9,000/year as a planning figure and verify with a broker who writes WUI policies.
Some properties in the highest fire zones may require a CA FAIR Plan policy plus a wraparound DIC — the combined annual premium for a 3,000 sqft home in those zones can exceed $10,000/year. The /fire-rebuild-guide-ventura-county page walks the FAIR Plan + DIC structure in detail.
HOA dues in Simi Valley
Most older Simi neighborhoods have no HOA. Newer master-planned communities have HOAs ranging from $80-$400/month: Wood Ranch master HOA roughly $150-$250/month with some sub-associations adding $50-$150 on top; Big Sky HOA roughly $200-$300/month; Sycamore Grove $80-$180/month; smaller condo communities $300-$500/month.
Always pull the HOA disclosure during the 17-day contingency period. The disclosure shows current dues, special assessments outstanding or anticipated, reserves balance, and any pending litigation. Some HOAs with deferred maintenance carry near-term assessment risk that materially changes the monthly carrying cost — verify before contingency removal.
Putting it all together — a worked PITI+Mello+HOA example
Take a $1.1M home in Wood Ranch with 20% down at 6.75% rate, 30 year term. Loan $880,000. Property tax 1.15% of $1.1M = $12,650/year = $1,054/month. Mello-Roos $2,800/year = $233/month. Insurance $4,200/year (Wood Ranch is in elevated fire exposure) = $350/month. HOA $200/month.
P&I on $880,000 at 6.75% / 30yr = $5,706/month. Plus tax $1,054 + Mello-Roos $233 + insurance $350 + HOA $200 = total monthly $7,543. The $1.1M Wood Ranch home costs the buyer about $7,543/month all-in, before any utilities.
Compare to the same $1.1M home in older established Simi (Texas Tract or Indian Hills): no Mello-Roos, no HOA, baseline insurance $2,400/year. Same P&I $5,706 + tax $1,054 + insurance $200 = $6,960/month. The Wood Ranch carrying cost is $583/month higher — about $7,000/year — for the same purchase price, due to Mello-Roos, HOA, and elevated insurance.
This is the math that often surprises buyers comparing a Wood Ranch home to a Texas Tract home at the same price point. Run the calculator with the actual CFD and HOA numbers for the specific home before deciding.
Rate sensitivity — how monthly changes with interest rate
Rate sensitivity is one of the most important things to model before you commit. At $885,000 home with 20% down ($708K loan, 30 year term), here is how monthly P&I changes by rate: at 5.5% rate, P&I is $4,021/month; at 6.0% it's $4,246; at 6.5% it's $4,475; at 6.75% (current) it's $4,592; at 7.0% it's $4,710; at 7.5% it's $4,950; at 8.0% it's $5,195.
Each 0.25% rate change moves the monthly by roughly $115-$125 on this loan size. Over a 30-year hold, the cumulative interest difference between 6.0% and 7.0% on a $708K loan is roughly $200,000. Rate matters more than most buyers realize on long-hold purchases.
If rates fall meaningfully after purchase (typically 0.75-1.0% drop), refinancing can recover some of the difference. Refinance closing costs typically run $4,000-$8,000, so the breakeven on a refi is usually 18-36 months at the lower payment. Discuss with your lender before locking on the assumption that you'll refinance — sometimes the original loan terms include points or buydowns that change the math.
Debt-to-income (DTI) and what you can actually afford
Lenders qualify based on debt-to-income ratio. Conventional loans typically cap front-end DTI (housing payment / gross monthly income) at 28-31% and back-end DTI (housing + all other debt / gross income) at 43-50% depending on loan program and credit profile. Jumbo loans typically tighter.
Worked example: gross household income $20,000/month, no other debt. At 31% front-end cap, max housing payment is $6,200/month. Subtract estimated tax, insurance, HOA, Mello-Roos from $6,200 to get max P&I — for a Wood Ranch property with $1,800/month in tax/ins/HOA/Mello, max P&I is $4,400, which at 6.75% supports a loan of about $678K, which at 20% down corresponds to a max purchase price around $848K.
The calculator on this page helps you back into this number. Start from the monthly you can carry and work backward to the price, rather than the other way around. This is the analysis most buyers skip and most lenders won't volunteer.
What I tell buyers about payment math
What I tell buyers: always run the full PITI plus Mello-Roos plus HOA before writing an offer. The P&I-only number is misleading in any Ventura County master-planned community. The full monthly is what the underwriter uses for your debt-to-income ratio, and it's what shows up on your bank statement every month.
Get pre-approved by a lender who knows the local CFD and insurance landscape — they will model the full monthly correctly. If your pre-approval comes back at a price you can't actually carry with full PITI+Mello+HOA, you have a problem to solve before you start shopping.
Run sensitivity scenarios. What does the monthly look like at 7.5% rate (rates could rise) or 5.5% (rates could fall)? What if Mello-Roos is $5,500 instead of $2,800 (Big Sky vs Wood Ranch)? The decision quality is much better when you understand the range, not just the point estimate.
Frequently Asked Questions
How accurate is the Simi Valley mortgage calculator?
Accurate for planning — the P&I math is the standard amortization formula. The tax, HOA, Mello-Roos, and insurance lines are only as accurate as the inputs. Pull the actual property tax bill from the Ventura County Assessor and the actual HOA disclosure for accurate numbers on a specific home. Final binding numbers come from your lender's Closing Disclosure.
Does this calculator include PMI?
No. For down payments under 20%, add roughly 0.3-0.8% of loan amount divided by 12 to the monthly. Exact rate depends on credit score and LTV. Your lender can quote the precise PMI for your scenario.
What property tax rate should I use for Simi Valley?
1.13-1.18% effective is typical including voter-approved bonds. The calculator default of 1.15% is a reasonable planning figure. For exact rate on a specific parcel, look up the secured tax bill at the Ventura County Assessor portal.
Does Wood Ranch have Mello-Roos?
Yes — most Wood Ranch sub-tracts carry CFD assessments of $1,500-$3,500/year. Specific amount depends on the sub-tract within Wood Ranch. Big Sky runs higher ($2,500-$5,500/year). Verify the actual CFD line on the parcel's tax bill before relying on any specific figure.
What insurance number should I use for a Simi Valley home?
Baseline mid-Simi (outside Very High Fire Hazard Severity Zones) is $2,000-$3,200/year in 2026. Wood Ranch, Big Sky, Long Canyon, and hillside edges in VHFHSZ zones commonly run $4,500-$10,000+/year. Properties requiring CA FAIR Plan + DIC can exceed $10,000/year. Get a quote from a broker who writes WUI policies in your specific zone.
