Conventional Loan Calculator: How PMI, Your Credit Score, and the Conforming Limit Shape the Payment
A conventional loan calculator clears up the most expensive myth in home buying: that you need 20% down. You don't — 3% is the real floor for a conventional mortgage on a primary home. What 20% actually buys you is an escape from private mortgage insurance (PMI). And once you see how PMI is priced and how quickly it disappears, the whole down-payment decision flips from "save for years" to "run the numbers."
Three Percent Down Is Real — 20% Just Skips the PMI
The minimum down payment on a conventional loan is 3% for a primary residence through programs like Fannie Mae's HomeReady and Freddie Mac's Home Possible. On a $400,000 home, that's $12,000 — not $80,000. The 20% number lives in everyone's head because it's the threshold where PMI stops being required, not because lenders demand it to approve you.
Here's the trade-off in plain terms. Put less than 20% down and you pay PMI every month until your balance falls to 80% of the home's value. Put 20% down and there's no PMI from day one. So the real question isn't "can I buy with less than 20%" — you can. It's "is the PMI worth keeping my cash," and for a lot of buyers it is. The down payment calculator lets you test each level against your savings.
Why Conventional PMI Is Temporary (and That Changes the Math)
This is the one feature that separates a conventional loan from an FHA loan. Conventional PMI cancels. Under the federal Homeowners Protection Act, your lender must drop PMI automatically once your balance reaches 78% of the original purchase price, and you can request cancellation at 80%. FHA mortgage insurance, by contrast, usually sticks around for the life of the loan.
That makes PMI a temporary cost, not a permanent one — and it reshapes the down-payment decision. On a $450,000 home with 10% down, PMI runs roughly $90 a month and, on the amortization schedule alone, drops off somewhere around year 9 to 11. Total PMI paid: about $8,500, then it's gone for good. Weigh that against handing the lender an extra $45,000 up front just to skip it. If your home appreciates even modestly, you can request removal earlier with a fresh appraisal showing 20% equity — plenty of buyers shed PMI in three to five years. For a closer look at that cancellation timeline, the PMI calculator isolates exactly that number.
Your Credit Score Sets Your PMI Rate
Most buyers don't realize PMI isn't a flat fee — it's priced by your credit score and your loan-to-value ratio together. A strong score doesn't just lower your interest rate; it slashes your mortgage insurance. The spread is enormous. Here are approximate annual PMI rates for a 30-year fixed loan, as a percent of the loan amount:
| Credit Score | 5% Down (95% LTV) | 10% Down (90% LTV) | 15% Down (85% LTV) |
|---|---|---|---|
| 760+ | 0.30% | 0.23% | 0.19% |
| 740–759 | 0.38% | 0.27% | 0.20% |
| 700–719 | 0.62% | 0.41% | 0.27% |
| 680–699 | 0.78% | 0.52% | 0.34% |
| 620–639 | 1.24% | 0.84% | 0.54% |
Run the math on a $380,000 loan at 5% down. A 760 score pays 0.30% — about $95 a month. A 620 score pays 1.24% — roughly $392 a month for the identical house. That's $297 a month, or $3,564 a year, riding entirely on credit. If your score sits near a bucket edge, nudging it up 20 or 30 points before you apply can pay off faster than almost any other prep work you do.
The Down Payment Ladder: 3%, 5%, 10%, 20%
Every rung up the down-payment ladder does two things at once: it shrinks your loan, and it lowers (then eliminates) your PMI rate, because a bigger down payment moves you into a cheaper LTV band. Take a $450,000 home at 6.5% with a 740 score:
| Down Payment | Loan Amount | PMI Rate | PMI / month |
|---|---|---|---|
| 3% ($13,500) | $436,500 | 0.56% | ~$204 |
| 5% ($22,500) | $427,500 | 0.38% | ~$135 |
| 10% ($45,000) | $405,000 | 0.27% | ~$91 |
| 20% ($90,000) | $360,000 | 0% | $0 |
Look at the jump from 3% to 5% down. An extra $9,000 in cash cuts PMI by about $69 a month — roughly a 9% annual return on that $9,000 in insurance savings alone, before you even count the smaller loan and lower interest. That's why 5% is often the sweet spot: it's reachable, and it lands you in a meaningfully cheaper PMI band than the bare 3% minimum.
Worked Example: $450,000 Home, 10% Down, 740 Score
Let's build a full conventional payment from scratch. Home price $450,000, 10% down, 6.5% rate, 30-year term, 740 credit score.
- Down payment: $450,000 × 10% = $45,000
- Loan amount: $450,000 − $45,000 = $405,000 (90% LTV)
- Principal & interest: about $2,560/month
- PMI: $405,000 × 0.27% ÷ 12 ≈ $91/month
- Taxes + insurance: ($5,400 + $1,800) ÷ 12 = $600/month
- Full payment: roughly $3,251/month
Now the part that matters most. That $91 PMI isn't forever. By scheduled amortization, the $405,000 balance reaches 80% of the original $450,000 value (the $360,000 mark) around year 8, and auto-cancels at the $351,000 mark near year 9. Total PMI over that stretch: roughly $8,500 — after which the payment drops to about $3,160. Benchmark this against a standard run on the mortgage calculator to see the same loan without the insurance line.
Conforming vs. Jumbo: The Limit That Splits Two Loan Worlds
A conventional loan is either "conforming" or "jumbo," and the dividing line is the conforming loan limit the Federal Housing Finance Agency sets each year. Stay at or under that limit and your loan can be backed by Fannie Mae or Freddie Mac, which keeps rates lower and underwriting more standardized. Cross it and you're in jumbo territory.
Jumbo loans aren't worse — they're stricter. Expect a higher minimum credit score (often 700+), larger cash reserves (sometimes 6 to 12 months of payments in the bank), and a bigger down payment, frequently 10% to 20%. The practical takeaway: if your loan amount lands just above the limit, putting a little more down to slip back under it can unlock easier approval and better pricing. High-cost counties get a higher ceiling, so confirm the figure for your area at the FHFA's official limit lookup before assuming a price requires a jumbo.
Conventional vs. FHA: A Credit-Score Decision
For most buyers, the real choice is conventional versus FHA, and it comes down to your credit score more than anything else. Conventional rewards strong credit; FHA forgives weak credit.
| Factor | Conventional | FHA |
|---|---|---|
| Minimum credit score | 620 (best pricing 740+) | 580 (3.5% down) |
| Minimum down payment | 3% | 3.5% |
| Mortgage insurance | 0.19%–1.61%/yr, cancelable | 0.55%/yr, often for life |
| Insurance ends | Automatic at 78% LTV | Refinance or 11-year rule |
| Upfront insurance fee | None | 1.75% financed into loan |
The crossover sits around a 680 score. Below it, FHA's pricing and easier approval usually win on monthly cost, even with its lifetime insurance. Above it, conventional's lower, cancelable PMI pulls ahead — and it skips the 1.75% upfront premium FHA finances into your loan. If your score is borderline, run both: the FHA loan calculator shows the MIP side of the comparison, and veterans should also weigh the VA loan calculator, which offers zero down and no monthly mortgage insurance at all.
Mistakes That Cost Conventional Buyers Thousands
- Draining savings to reach 20%.Buyers often empty their emergency fund to avoid PMI. But PMI on a 10%-down loan might total $8,500 and then vanish — far less than the $45,000 of cash you'd tie up in the walls. Keep a cushion; let PMI cancel on its own.
- Not requesting PMI cancellation at 80%. Lenders only auto-cancel at 78%. If you reach 80% early through extra payments or appreciation, you have to ask. Twenty minutes on the phone can stop a $90–$200 monthly charge months sooner.
- Ignoring how much credit moves PMI.A 60-point score gap can quadruple your PMI rate. On a $380,000 loan that's $3,500+ a year. Pull your credit before you shop and fix easy errors first — the home affordability calculator shows how that monthly swing changes the price you can carry.
- Forgetting the conforming limit. A loan $5,000 over the limit becomes a jumbo with tougher rules. A slightly larger down payment can keep you conforming — check before you assume you need a jumbo product.
When a Conventional Loan Isn't Your Best Move
A conventional loan is the default for a reason — but it's not always the cheapest path. Look hard at the alternatives when:
- Your credit score is below 660.FHA often beats conventional on both rate and PMI in the 580–659 range, even though its insurance lasts longer. Compare total cost over the years you'll actually own the home, not just the first payment.
- You qualify for a VA loan.Eligible veterans and service members get zero down and no monthly mortgage insurance — a structure conventional simply can't match.
- You're buying in a rural area. A USDA loan offers zero down with a low 0.35% annual fee in eligible zones. If your address qualifies, it can undercut a low-down conventional loan. The USDA loan calculator checks the cost side once you confirm eligibility.
Before you commit, ask your lender for a conventional quote alongside any program you qualify for, and have them spell out when each one's mortgage insurance ends. The starting payments often look close. The real gap shows up a few years in — when one borrower's PMI has already dropped off and another's is still on the bill. That's the number the headline rate never shows you, and it's exactly what this calculator is built to surface.
