Same numbers, different rules: a decoder
There are at least four common home-buying rules in India. They share numbers, but the numbers mean different things.
In one rule, 20 is how much you pay upfront. In another, it is how many years your loan runs. 40 is a spending limit in one rule and an upfront payment in two others.
Mix them up and you can follow "the rule" carefully and still end up somewhere none of the rules would allow.
What each number means
| Rule | Price limit | Paid upfront | Loan length | Housing EMI | All EMIs |
|---|---|---|---|---|---|
| 20/30/40 | — | 20% | — | 30% | 40% |
| 28/36 (US) | — | — | — | 28% | 36% |
| 5/20/30/40 | 5× yearly | 40% | ≤20 yrs | 30% | — |
| 3/20/30/40 | 3× yearly | 40% | ≤20 yrs | — | 30% |
Three clashes are worth knowing about.
"20" changes meaning. It is the upfront payment in 20/30/40, but the loan length in both four-part rules. Someone reading "20" as the upfront amount while following 3/20/30/40 would pay 20% instead of 40%, half the cash the rule intends.
"40" changes too. It caps all your EMIs in 20/30/40. In the other two, it is the minimum you pay upfront. One limits borrowing and the other requires savings.
"30" is not always the same 30. In two rules it covers housing only. In 3/20/30/40 it covers every EMI you have, including car and personal loans. The same number is much stricter there.
The biggest gap: how much you pay upfront
20% versus 40% is not a small detail. It is the largest difference between these rules in the cash you need in hand.
On an ₹80 lakh flat, the stricter rules want ₹32 lakh in hand instead of ₹16 lakh. And neither figure includes stamp duty, registration or interiors, which add roughly ₹6.6 lakh more.
The loan-length limit
Both four-part rules say to keep the loan to 20 years or less. This part gets the least attention and costs the most to ignore. Here is a ₹37.2 lakh loan at 7.5%:
| Loan length | EMI | Total interest | vs 20 years |
|---|---|---|---|
| 15 years | ₹34,522 | ₹24.9L | −₹9.9L |
| 20 years | ₹30,000 | ₹34.8L | — |
| 30 years | ₹26,038 | ₹56.5L | +₹21.7L |
Stretching from 20 to 30 years saves about ₹4,000 a month and costs about ₹21.7 lakh extra. Lenders rarely show you both numbers side by side.
One set of limits to use
Take the sensible part of each rule and you get one clear set of limits instead of four competing ones:
Aim for 3×. Treat 5× as the ceiling, and only with a big upfront payment.
20% is the minimum. More upfront means less interest overall.
A longer loan is not cheaper. Same debt, more interest.
EMI plus maintenance and property tax, not the EMI alone.
Every loan you have. Leave room for the rate to rise.
Duties, registration and interiors. Budget for these before you commit.
Every one of these is a maximum, not a target. Passing all of them does not mean buying is a good idea. It only means it is unlikely to strain your finances.