Safe Installments: The DTI Formula and the Biggest Monthly Payment Your Salary Can Handle

Tim Moneysaurus · 2026-07-17

Before you sign up for any new installment, whether it is a motorbike, a phone, or a mortgage, the question is always the same: can I actually afford this? The trouble is that the feeling of affording it is unreliable. The numbers are honest. There is one simple formula banks around the world use to answer that question, and you can run it yourself before signing anything.

The rule: 28/36, or its local version, 30 percent

DTI, or debt-to-income ratio, is just your total monthly debt payments divided by your monthly income. The best-known global benchmark is the 28/36 rule. According to Chase, you should spend no more than 28 percent of your gross income on housing, and no more than 36 percent on all your debts combined, housing included. That 36 percent figure is your DTI.

In Indonesia the benchmark is even tighter and easier to remember: keep total installments under 30 percent of monthly income. This is not just influencer advice. Certified financial planner Rista Zwestika cites 30 percent as the healthy ceiling (ANTARA), and the regulator OJK has turned it into law: starting in 2026, under POJK 40/2024 and SEOJK 19/2025, total peer-to-peer lending debt is capped at 30 percent of income (Kompas).

So the target is clear. Keep total installments at 30 percent, and for a mortgage keep the housing portion close to 28 percent.

Work out your own ceiling

The one rule that matters here: use your stable monthly income, not a half-finished current month or a bonus that may never come again.

Example. Your stable salary is Rp8 million a month.

So any new installment should stay under Rp1.4 million a month. If a salesperson offers you a plan at Rp1.8 million, the math is already a red light, no matter how manageable it feels.

Notice the paylater in that table. People forget it constantly. But every monthly payment counts, no exceptions, including paylater, credit cards, and online loans. Missed paylater payments are even recorded and add to the debt load banks assess (Bank Mega).

Fitting your cashflow is not the same as being safe

This is the step most people skip. An installment can clear the 30 percent test and still be risky if you have no cushion.

OJK and financial planners agree: hold an emergency fund of at least 3 to 6 months of expenses if you are single, 6 to 9 months if you are married, and 9 to 12 months if you have children (Bank Sinarmas).

Imagine your new installment lands neatly at 30 percent, but your emergency savings cover only one month. The moment something happens, a broken bike, a layoff, a sick parent, that installment turns into a weight that crushes you. The verdict: it fits your cashflow, but it is not yet safe. The fix is not to kill the dream, just to delay it a little. Build three months of emergency savings first, or put down a larger down payment so the installment shrinks.

If a mortgage is the goal: guard your SLIK

If you are aiming for a house, one more thing has to be clean, namely your SLIK OJK record (formerly BI Checking). Every installment, paylater and online loans included, is logged there with a collectibility score from 1 to 5. A 1 means current. Once you slip to a 3 or worse from late payments, banks will almost certainly reject your mortgage (CNBC Indonesia).

So three to six months before you apply, tidy everything up: pay off paylater, pay every installment on time, and if you can, reduce consumer debt so your DTI drops and the room for a home loan grows.

The takeaway

A safe installment is not about whether it feels affordable. It is about numbers: total installments under 30 percent of stable income, at least three months of emergency savings, and a clean SLIK. To keep those numbers in view, you need to know exactly where your money goes each month. Logging it can be as simple as texting "paid motorbike installment 700k" to Moneysaurus on WhatsApp and letting your total build itself. Before you sign the next one, do the math first. Numbers never lie.

Sources: the 28/36 rule from Chase; the 30 percent installment ceiling from ANTARA (Rista Zwestika, CFP) and OJK's 2026 lending rule (POJK 40/2024 and SEOJK 19/2025) via Kompas; paylater as debt from Bank Mega; SLIK OJK collectibility scoring from CNBC Indonesia; emergency fund sizing from Bank Sinarmas.