Why the Myth Exists
The 20% rule survives because it points to something real. The CFPB says that if a buyer cannot make a 20% down payment, lenders usually require private mortgage insurance or an FHA, VA, or USDA loan.
The CFPB describes PMI as insurance a borrower might need to buy when taking out a conventional loan with less than 20% down. PMI protects the lender, not the borrower, and can increase loan costs.
So, the rule is useful. It is just incomplete.
When the 20% Rule Helps
The 20% rule helps when the buyer can still cover closing costs, moving costs, repairs, and an emergency cushion after closing.
It can be especially useful when:
- The monthly payment is tight before mortgage insurance.
- The buyer wants lower fixed housing costs.
- The buyer still has enough cash after closing.
- The lower loan balance improves the loan terms.
When It Gets Too Rigid
The rule gets too rigid when it pushes a buyer to drain cash or wait for years without comparing the cost.
The CFPB says many loans require at least 3% down, and many require 5% or more. It also says low- or no-down-payment options may be available, but usually come at an increased cost.
That does not mean a smaller down payment is automatically better. It means the real comparison is bigger than one rule.
The Math: A $400,000 Example
Assume a $400,000 home, a 30-year fixed loan, and an illustrative 6.75% interest rate. This is not a quote. Taxes, homeowners insurance, HOA dues, maintenance, closing costs, and lender fees are excluded. For sub-20% down examples, PMI is shown as an illustrative 0.50% to 1.00% of the starting loan balance per year.
| Down payment | Cash down | Starting loan | Monthly P&I | Illustrative monthly PMI | P&I + illustrative PMI |
|---|---|---|---|---|---|
| 20% | $80,000 | $320,000 | $2,076 | $0 | $2,076 |
| 10% | $40,000 | $360,000 | $2,335 | $150-$300 | $2,485-$2,635 |
| 5% | $20,000 | $380,000 | $2,465 | $158-$317 | $2,623-$2,781 |
| 3% | $12,000 | $388,000 | $2,517 | $162-$323 | $2,678-$2,840 |
In this example, 5% down keeps $60,000 more cash before closing costs than 20% down. It also raises principal and interest by about $389 per month before mortgage insurance. With the illustrative PMI range, the monthly difference versus 20% down could be roughly $547-$705 before taxes and insurance.
That is the tradeoff. The smaller down payment keeps more cash available. The larger down payment lowers monthly pressure.
What Basis Would Model
The better question is:
What happens to the household plan if the buyer puts 20%, 10%, 5%, or 3% down?
A useful model compares:
- Cash left after down payment and closing costs.
- Monthly payment pressure.
- PMI or mortgage insurance cost.
- Emergency fund coverage after closing.
- Time to reach 20% equity.
- Risk of waiting while rent, home prices, income, or rates change.
- Other uses for cash.
This is where the myth becomes math. "20% down" is one input, not the whole answer.
Key takeaways
- 20% down can reduce loan cost and payment pressure, but it is not a universal requirement.
- Less than 20% down can mean private mortgage insurance or a different loan structure.
- The better question is what each down payment does to cash left, monthly payment, insurance cost, and time.
Frequently asked questions
Is 20% down required to buy a house?
No. Down payment requirements vary by loan and lender. The 20% threshold matters because a conventional loan with less down may require private mortgage insurance or another loan structure.
What is the lowest down payment on a mortgage?
It depends on the loan and lender. The CFPB says many loans require at least 3% down, and many require 5% or more. Program eligibility, credit profile, income, property type, lender rules, and pricing still matter.
Is PMI always bad?
No. PMI is a cost, but it is not automatically a mistake. It can let a borrower buy with less cash upfront. The math depends on the PMI amount, how long it lasts, cash reserves, and what happens if the buyer waits.
What should a buyer compare before deciding?
A useful comparison includes total cash to close, cash left after closing, monthly payment pressure, PMI or mortgage insurance, repair and moving costs, and how long it may take to save more.
Sources
- CFPB: What kind of down payment do I need? - Verifies that down payment requirements vary and that less than 20% can mean PMI or another loan type
- CFPB: Determine your down payment - Verifies cash-left considerations, closing cost context, and the 3%, 5%, 10%, and 20% down payment framing
- CFPB: What is private mortgage insurance? - Verifies what PMI is, who it protects, when it can apply, and why it can increase loan cost
Sources were reviewed on June 18, 2026 unless noted.
Educational only
Basis is not a financial adviser, investment adviser, broker, accountant, attorney, lender, or mortgage broker.