Interest-free instalments: how they really work
An interest-free instalment plan splits a purchase into equal payments at no extra cost — as long as every payment is made on time. The catch is rarely the interest. It is how much of your credit limit the plan holds, and how many plans you are paying at once.
How an instalment plan works
The price is divided into equal monthly payments, and each statement includes one. If each one is paid in full and on time, the price never grows.
What surprises people is the credit limit. On a card, the whole price is held against your limit the day you buy, and released one payment at a time: a $1,200 phone on 12 payments uses $1,200 of your limit today, and $100 less each month after.
In Mexico this is meses sin intereses, offered by banks and stores on almost anything. In the US the nearest things are a card issuer’s instalment plan, a 0% promotion, and buy-now-pay-later services.
Where plans go wrong: stacking
| Purchase | Price | Months | Each month |
|---|---|---|---|
| Television | $1,200 | 12 | $100 |
| Phone | $900 | 18 | $50 |
| Flights | $600 | 6 | $100 |
| Laptop | $1,500 | 12 | $125 |
| All four, each month | $375 |
None of these is large on its own. Together they take $375 from every statement for six months, $275 for the six after that, and $50 until the phone is paid off — before anything else is bought. Each new plan is judged by its own payment; the total is what the next year actually feels like.
If a payment is missed
On a card, the month’s instalment is part of what is due. Pay less than that and interest is charged on what is left — and, depending on the issuer, the plan can lose its 0%. The terms say which; read them before you agree, not after.
Deferred interest is not 0%
Store cards and medical financing often advertise “no interest if paid in full in 12 months”. That is deferred interest: interest builds up from the day you buy, and if any of the balance is left when the period ends, all of it is charged at once — on the original price, back to the first day.
| Deferred interest | 0% APR | |
|---|---|---|
| Paid in full in time | No interest | No interest |
| $50 left at the end | Interest on the whole original purchase, from the day you bought it | Interest on the $50, from then on |
| How it is worded | “No interest if paid in full” | “0% intro APR” |
Some issuers’ instalment plans charge a fixed monthly fee instead of interest. The fee is the cost, and it is shown before you accept.
Buy now, pay later
Pay-in-four services split a purchase into four payments over six weeks, usually with no interest. They are not on your card statement, which is what makes them easy to lose track of: each one is still a date money leaves your account. Some charge late fees, and their longer plans can charge interest.
When a plan is worth it
- The price on the plan is the same as paying at once. If paying at once is cheaper, the plan has a cost — compare them.
- You would buy it anyway, and spreading it keeps cash for the rest of the cycle.
- The total of all your plans — not just this one — still leaves room in every paycheck.
- You know the month it ends.
Doing it in TwoCoins
Any payment that repeats goes in once, as a commitment with the day it posts, and comes out of what is free in the cycle it lands in — never the whole price in the month you bought. Loans and plans with interest also take the number of payments, and show the month they end. In the Mexico market, meses sin intereses get their own kind of plan.