Flat rate vs APR: why a “5% flat” car loan really costs about 9%, and how to convert it

Two rates that sound the same and are not

A bank in Dubai advertises a car loan at “2.49% flat”. A bank in Karachi offers financing at “9% per annum”. A credit card charges “1.5% a month”. These three numbers are not on the same scale, and comparing them as if they were is how people end up paying almost twice the interest they thought they had agreed to.

The difference is what the rate is charged on.

A flat rate is charged on the full amount you borrowed, for every month of the loan, even though you are paying the loan back as you go. Borrow 100,000 at 4% flat over five years and the interest is 100,000 × 4% × 5 = 20,000, fixed on day one, and spread evenly over 60 payments of 2,000.

A reducing-balance rate, which is what APR means and what mortgages, credit cards and most Western loans use, is charged only on what you still owe. In month one you owe 100,000; by month 30 you owe about half, and the interest that month is about half as well.

Because the flat rate keeps charging on money you have already repaid, a flat rate always costs more than a reducing rate of the same number. Over a typical car loan it costs almost twice as much.

The conversion, with the numbers

The reducing rate that costs exactly the same as a flat rate depends only on the term, not on the amount. Here are the figures the converter on this site produces:

Flat rate	Over 3 years (36 months)	Over 5 years (60 months)
3%	5.68% APR	5.64% APR
4%	7.51% APR	7.42% APR
5%	9.31% APR	9.15% APR
6%	11.08% APR	10.85% APR
8%	14.55% APR	14.13% APR
9%	16.24% APR	15.71% APR

The rule of thumb that a flat rate is “about double” the reducing rate is close: the factor is between 1.75 and 1.9 for loans of two to seven years, a little higher for short loans and a little lower for long ones. Five percent flat is nine percent APR, not five.

Take the two advertisements above. The Dubai loan at 2.49% flat over three years is 4.74% APR. Pakistani car financing at 9% flat over five years is 15.71% APR; on PKR 1.5 million that is a monthly instalment of 36,250, against 31,138 if the 9% were a reducing rate, and about 675,000 of total profit against 368,000. The quoted number is the same in both cases. The cost is not.

How to do it by hand

If you want to check a figure without a calculator, the monthly payment of a flat-rate loan is easy:

payment = (amount + amount × flat rate × years) ÷ months

For 100,000 at 4% flat over 5 years: (100,000 + 20,000) ÷ 60 = 2,000 a month.

Finding the equivalent APR by hand is harder, because it is the rate at which 60 payments of 2,000 exactly repay 100,000, and that has no closed formula; the converter searches for it. But you can get close in your head with the approximation banks themselves used before calculators:

APR ≈ flat rate × 2 × months ÷ (months + 1)

For 4% over 60 months: 4 × 2 × 60 ÷ 61 = 7.87%, against the exact 7.42%. Good enough to see that “4%” is really “about 7.5%”, which is the decision that matters.

Why banks in the Gulf and Pakistan quote flat rates

Flat rates are not a trick in themselves; they are the older convention, and in several markets the normal one. They have three honest advantages for the lender and one for the borrower.

For the lender, the interest is known on day one, the instalment is a round figure that never changes, and the small number looks good in an advertisement next to a competitor’s reducing rate. For the borrower, the arithmetic is transparent: anyone can multiply the amount by the rate and the years and see the total cost, which is exactly what you cannot do with an APR.

Islamic financing adds a reason of its own. In a murabaha car purchase the bank buys the car and sells it to you at a fixed, agreed profit, paid in instalments. That profit is a sum of money, not a rate, so quoting it as a flat percentage of the price per year is the natural way to express it. The equivalent APR still exists and still tells you what the financing costs compared with a conventional loan; it is a measure of cost, not a statement about how the contract works.

The regulators know this too. The UAE Central Bank’s Regulation 29/2011 requires banks to calculate and declare rates on the reducing balance of the loan, and the State Bank of Pakistan’s product disclosure rules require the annual percentage rate (APR) to be disclosed for personal and auto finance. So the reducing-balance figure should be in the key facts sheet or the contract, usually in smaller type than the flat rate in the advertisement; find it before you sign.

What a flat rate means if you settle early

Here the two conventions bite in a way people rarely expect. Under a flat rate your instalments are equal and the interest is “spread evenly”, so after 30 of 60 months you might think you have paid half the capital and half the interest, and owe 50,000. You do not.

Banks work out the early-settlement balance with the equivalent reducing rate, the way the converter’s schedule shows: in the early months most of each 2,000 instalment is interest and little is capital. After 12 months of a 4% flat loan on 100,000 you still owe about 82,800; after 30 months about 54,600, not 50,000. Some lenders use the older “rule of 78” instead, which loads even more of the interest into the early months. Either way, the settlement figure is higher than the naive half, and on top of it most Gulf banks charge an early settlement fee of about 1% of the outstanding amount.

So if there is a real chance you will pay the loan off early, the flat rate is worse for you than its APR suggests, and a reducing-rate loan at the same APR would have been the better contract.

A short checklist before you sign

• Ask whether the rate is flat or reducing. If the word “flat” appears, or the rate seems low for the market, assume flat.
• Convert it. Multiply by about 1.8, or use the converter for the exact figure over your term.
• Compare the total amount payable between offers, not the rates: it is the one number that cannot mislead.
• Read the early-settlement clause: how the balance is worked out and what the fee is.
• Check that the APR equivalent is in the contract, as the regulator requires.

The figures here are arithmetic, not financial advice. Fees, insurance bundled into the instalment and processing charges change the real cost of a loan, so compare complete offers, in writing, from more than one lender.