What it means
Adjustable-rate loans have two parts to their pricing. The index is a published market rate that moves on its own, and the margin is a fixed number of percentage points the lender adds on top, agreed at the start and unchanged for the life of the loan.
Add the two together and you get the fully indexed rate. It is the rate the loan would charge today in the absence of any discount, and it is the target the actual rate moves towards each time the loan resets.
The reason the fully indexed rate matters is that the rate on the loan documents is often lower. Many adjustable-rate mortgages and business facilities open with a discounted introductory rate, and the fully indexed rate shows the borrower what the payment jumps to once that discount falls away.
Caps complicate the picture in the borrower's favour. Periodic caps limit how much the rate can rise at any single reset and lifetime caps limit the total rise, so the rate charged can sit below the fully indexed rate for a while even after the introductory period ends.
Lenders in many markets are required to assess affordability at the fully indexed rate rather than the introductory rate. That is a sensible discipline for any borrower to copy: work out whether the payment is affordable at the full rate before signing, not at the discounted one.
In practice
Real-world examples.
Example
A first-time buyer is offered a mortgage advertised at 4.50% but is told the fully indexed rate is 6.90%, made up of a 4.15% index plus a 2.75% margin. The lender stress tests affordability at 6.90%, which reduces the amount she can borrow by about a fifth.
Example
A restaurant group draws a $2,000,000 variable-rate expansion facility priced at the benchmark plus 3.50%. With the benchmark at 4.00%, the fully indexed rate is 7.50%, and the finance director builds the annual budget on $150,000 of interest rather than the discounted first-year figure.
Example
A mortgage broker reviewing a client's existing loan spots that the index has fallen since the loan reset, so the fully indexed rate is now 6.25% while the client is still paying 7.10% because the rate only adjusts annually. She notes the next reset date and diarises a review.
Formula
Calculation
Fully indexed rate = Current index rate + Margin
Priya takes a $300,000 adjustable-rate mortgage. The introductory rate is 5.00% for the first two years, the loan is tied to a benchmark index currently at 4.25%, and the contractual margin is 2.75%.
Fully indexed rate = 4.25% + 2.75% = 7.00%.
Comparing the monthly interest cost at each rate makes the gap concrete:
Interest at the introductory rate = $300,000 x 5.00% / 12 = $1,250 per month.
Interest at the fully indexed rate = $300,000 x 7.00% / 12 = $1,750 per month.
Difference = $1,750 - $1,250 = $500 more per month, or $6,000 a year.
The loan has a 2 percentage point periodic cap and a 5 percentage point lifetime cap. At the first reset the rate can rise from 5.00% to at most 7.00%, so the fully indexed rate is reachable in one step, and the lifetime ceiling of 10.00% only binds if the index climbs above 7.25%.Case study
Seen in the real world.
Bramble Court Dental, a fictional practice created purely to illustrate the point, borrowed $600,000 on an adjustable-rate commercial mortgage to buy its premises. The introductory rate was 4.50%, and the practice owner budgeted around that number because it was the figure printed at the top of the offer letter.
The fully indexed rate at the time was 7.20%, being an index of 4.20% plus a margin of 3.00%, and it was disclosed on page four of the same offer. When the introductory period ended, the annual interest bill moved from $27,000 to $43,200, an increase of $16,200 a year that the practice had never modelled.
The illustrative fix was mundane but effective. The owner refinanced part of the balance onto a fixed rate and, from then on, every loan comparison in the practice was done on the fully indexed rate with the introductory rate treated as a temporary rebate rather than the real price.
Watch out
Common mistakes.
- Budgeting on the introductory rate because it is the number printed most prominently. The introductory rate is temporary, and the fully indexed rate is the price the loan is genuinely built around.
- Assuming the margin can change if the borrower's circumstances improve. The index moves freely but the margin is fixed in the contract, so improving the rate usually means refinancing rather than renegotiating.
- Believing that a rate cap removes the risk. Caps slow the increase, they do not prevent the rate reaching the fully indexed level once the index has settled at a higher point.
Questions
People also ask.
Is the fully indexed rate the same as the rate I actually pay?
Not necessarily, because introductory discounts, periodic caps and lifetime caps can hold the charged rate below it, and the two only match once those constraints stop biting.
Can the fully indexed rate fall?
Yes, it falls whenever the underlying index falls, since the margin is fixed, which is why variable-rate borrowers benefit when benchmark rates decline.
Where do I find the margin on my loan?
It is stated in the loan agreement, usually in the interest rate or rate adjustment section, and it should also appear in the disclosure documents given before completion.
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