Book a fixed deposit at seven per cent and it pays seven per cent until the day it matures, whatever happens to interest rates in the meantime. Take a mortgage from the very same bank, though, and its rate can rise or fall several times over the years you spend repaying it. Same bank, same customer, two rates that behave in opposite ways, and the difference isn’t arbitrary.
It comes down to what kind of contract each one is, and who is meant to carry the risk of rates moving. Once that’s clear, the puzzle dissolves, and you can see whose side each arrangement is really on.
Same bank, two rates behaving differently
The instinct is to assume a rule lets one change and freezes the other, but that isn’t it. Both rates could, in principle, be fixed or floating; it’s the standard structure of each product that decides how they behave. Deposits are almost always sold as fixed-rate arrangements, and long loans are almost always sold as floating ones.
That’s the whole of the mystery, really. The two aren’t governed by different standards of fairness, just by different types of agreement: one that locks a rate in and one that lets it move. Everything else follows from that single design choice.
Why is your deposit rate fixed for its whole term?
A fixed deposit is, by its nature, a fixed-rate promise. When you open one, the bank commits to paying you an agreed rate for the agreed term, and that commitment doesn’t change because the market later does. If rates fall the week after you book, you keep your higher rate; if they rise, you stay on your lower one until maturity.
That’s why a new FD opened tomorrow may carry a different rate from yours, while yours holds where it started. Each deposit is locked to the rate on the day it was booked. The bank has effectively agreed to bear whatever the market does for the life of that deposit, which is manageable because a deposit’s term is short.
Why a long loan is built to float
A home loan is the opposite kind of contract, and its length is the reason. Fixing a rate for twenty or thirty years would force the bank to guess where rates will be over an entire generation, a bet no lender takes without charging a heavy premium. So the standard home loan is a floating one, tied to a benchmark that moves with the market.
Because it floats, the rate resets as that benchmark changes, which is why your EMI can shift over the years. Your loan isn’t being singled out. This is how nearly every long retail loan works, kept transparent by rules that link the rate to an external benchmark you can see. A long loan floats for the same reason a short deposit stays fixed: the length of the commitment makes it the sensible way to build each one.
Who is actually carrying the interest-rate risk?
Underneath both is one question: when rates move, who absorbs it? That’s what separates your deposit from your loan. On the deposit, the bank carries the risk. It has promised to pay you a set rate, so if market rates climb, it’s paying you less than it would now to attract fresh money, and if they fall, it keeps paying you more.
On the floating loan, that risk sits with you. Your rate moves with the market, so when rates rise, your EMI rises with them, and the bank’s return holds regardless. This is the heart of the asymmetry. A fixed deposit hands the interest-rate risk to the bank; a floating loan hands it to the borrower. The rates behave differently because different parties are carrying the uncertainty in each.
Why the split suits the bank
From the bank’s side, the arrangement is neatly self-serving, and reasonably so. It wants a fixed, predictable cost on the money it borrows from depositors, which a fixed-rate deposit gives it over a manageable term. And it wants its return on very long loans to track the market, so its margin doesn’t get squeezed if its own costs rise.
Fixed on the short thing it owes you, floating on the long thing you owe it: that combination keeps the bank’s lending margin steady whichever way rates go. It isn’t a trick so much as a way of matching each contract’s rate to how long the bank has to live with it.
Does the asymmetry ever work in your favour?
It does, and which way depends entirely on where rates head. When rates fall, both sides treat you well: your existing deposit keeps paying the higher rate you locked in, while your floating loan gets cheaper as the benchmark drops. A falling-rate stretch is quietly good for someone who both saves and borrows.
When rates rise, the same structure works against you on both counts: your loan gets dearer, and your old deposit is stuck below what new deposits now earn. The fixed deposit protects you when rates fall and freezes you out when they climb; the floating loan does the reverse. Neither is designed for your benefit, but understanding which way each leans lets you read a rate move for what it means to you.
