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$0What a Loan Calculator Does
A loan is an agreement in which one party hands over a sum of money and the other commits to returning it, with interest, on agreed terms. This calculator turns those terms into the numbers that matter — what you pay each period, and what the borrowing costs you in total.
Enter the amount, the term, and the rate, and you'll see the payment figure alongside a full breakdown: how much of your money goes toward repaying the balance and how much goes to the lender as interest. That second number is usually the surprise, and it's the one worth checking before you sign anything.
The Three Ways a Loan Gets Repaid
Almost every loan falls into one of three repayment structures. They differ in when the money goes back to the lender, and that timing changes the total cost considerably.
Amortised
Equal payments at regular intervals until the balance reaches zero. Mortgages, car finance, student loans, and personal loans all work this way.
Deferred Payment
Nothing is paid until maturity, when the full balance and all accrued interest fall due in one lump sum. Common in short-term commercial lending.
Bond
The repayment amount is fixed in advance. The borrower receives a discounted sum upfront and pays the full face value at maturity.
When people say "loan" in everyday conversation, they almost always mean the first type. The other two behave differently enough that using the wrong model will give you a badly misleading answer.
Amortised Loans: Fixed Payments Over Time
This is the structure most borrowers encounter. Each payment is identical, but its composition shifts month by month. Interest is charged on whatever balance remains, so early payments are interest-heavy and later ones are almost entirely principal.
A = P × [ r(1+r)n ] / [ (1+r)n − 1 ]
A = Payment per Period · P = Principal · r = Periodic Interest Rate · n = Total Number of Payments
Worked Example
Borrow $100,000 over 10 years at 6% interest, compounded and repaid monthly:
| Payment every month | $1,110.21 |
| Total of 120 payments | $133,224.60 |
| Total interest | $33,224.60 |
| Interest as share of total | 25% |
Repaying $100,000 costs $133,224 in cash. That gap is the entire economics of lending, and it grows quickly with longer terms and higher rates.
Deferred Payment Loans: One Lump Sum at Maturity
Here nothing is repaid until the end. Interest compounds on the untouched balance for the entire term, so the amount owed grows steadily and the final bill is far larger than the sum borrowed. Many commercial and bridging loans are structured this way.
A = P × (1 + r)n
A = Amount Due at Maturity · P = Principal · r = Interest Rate per Period · n = Number of Periods
The same $100,000 at 6% over 10 years, compounded annually with no interim payments:
| Amount due at maturity | $179,084.77 |
| Total interest | $79,084.77 |
| Interest as share of total | 44% |
Identical principal, identical rate, identical term — yet the interest bill is more than double the amortised version. Nothing is chipping away at the balance, so interest keeps compounding on the full amount.
Balloon loans sit somewhere between the two, with modest periodic payments and a large final one. This model covers only loans with a single payment of everything at the end.
Bonds: Working Backwards From a Fixed Payout
Bonds reverse the usual question. Rather than asking what a given sum will cost to repay, you start with the amount due at maturity — the face or par value — and calculate what it's worth today.
P = A / (1 + r)n
P = Amount Received Today · A = Face Value at Maturity · r = Interest Rate per Period · n = Number of Periods
A bond paying $100,000 in 10 years, discounted at 6% annually:
| Amount received when the loan starts | $55,839.48 |
| Total interest | $44,160.52 |
Coupon and Zero-Coupon Bonds
Coupon bonds pay interest at set intervals — usually annually or semi-annually — calculated as a percentage of face value. Zero-coupon bonds pay nothing along the way. Instead they're sold well below face value, and the investor's return is the difference collected at maturity. This calculator models the zero-coupon case.
Once issued, a bond's market price moves with interest rates and broader market conditions. That fluctuation affects what someone will pay for it today, but not what the issuer owes at maturity — the face value is fixed from the start.
Three Terms That Decide What You Pay
Interest Rate
Interest is the lender's return, quoted as a percentage of the amount borrowed. Loans are usually advertised as APR, the annual percentage rate, which folds in both interest and mandatory fees — making it the fairer basis for comparing offers. Savings products are quoted as APY, the annual percentage yield, which accounts for compounding. Confusing the two makes a loan look cheaper than it is.
Compounding Frequency
Compound interest accrues on the original principal and on interest already added. The more often that calculation runs, the more you owe. Monthly compounding is standard for consumer loans; annual compounding costs less, daily costs more, all else equal.
Loan Term
Term is the repayment window. Extending it lowers each payment because the balance is spread across more of them — but it also keeps the debt outstanding longer, which means more interest overall. Shortening the term does the reverse. The right choice depends on whether your constraint is monthly cash flow or total cost.
Secured and Unsecured Borrowing
Consumer loans divide along one line: whether an asset backs the debt. That single distinction drives the rate you're offered, the amount available, and how likely you are to be approved.
Secured Loans
An asset is pledged as collateral and the lender registers a legal claim against it. Default and they can seize it — a repossessed car, a foreclosed home. Lower risk for the lender means lower rates, larger sums, and easier approval for you. If the asset sells for less than the outstanding debt, you can still owe the shortfall.
Unsecured Loans
No collateral, so lenders rely entirely on your financial profile. Credit cards, personal loans, and most student loans fall here. Expect higher rates, lower limits, and shorter terms. Weaker applicants may be asked for a co-signer who becomes liable if payments stop.
Missed payments on an unsecured loan don't put an asset at risk, but the account can be passed to a collection agency and the damage to your credit file will follow you into every future application.
How Lenders Judge an Application
Without collateral to fall back on, lenders assess creditworthiness through a framework known as the five C's:
- Character — your repayment history, credit file, employment record, and any outstanding legal or financial issues.
- Capacity — whether your income comfortably covers the new payment alongside existing debts, measured as a debt-to-income ratio.
- Capital — savings, investments, or a deposit that show you have resources beyond monthly earnings.
- Collateral — the asset securing the loan, where one exists. Applies to secured borrowing only.
- Conditions — the wider lending climate and what the money is actually for. A defined purpose reads better than an open-ended request.
Getting a Better Deal
- Compare APR, never the headline rate. Two loans quoting the same interest can differ substantially once arrangement fees are included.
- Get quotes from at least three lenders. Banks, credit unions, and online lenders price the same profile differently, and credit unions often undercut the rest.
- Tidy your credit file before applying. Paying down revolving balances and disputing errors a few months ahead can move you into a cheaper pricing tier.
- Take the shortest term you can comfortably service. Every additional year adds interest, even when the monthly figure looks more manageable.
- Check for early repayment charges. Some agreements penalise overpayment, which cancels out the benefit of clearing the debt early.
- Borrow only what the purpose requires. Approved limits are set by what you can service, not by what you need — the two are rarely the same.
Frequently Asked Questions
APR is the annual percentage rate on borrowing and includes interest plus mandatory fees, which makes it the right figure for comparing loan offers. APY is the annual percentage yield on savings and reflects the effect of compounding. Lenders quote APR; deposit accounts quote APY.
Because repayment structure and compounding frequency both matter. An amortised loan reduces the balance with every payment, so interest is charged on a shrinking amount. A deferred loan leaves the full balance in place until maturity, letting interest compound on the whole sum the entire time — which is why the example above costs more than twice as much.
A shorter term costs less overall and often carries a lower rate, but demands more each month. A longer term eases monthly pressure at a higher total price. If the shorter payment would leave no room for emergencies, take the longer term and overpay voluntarily when you can — provided the agreement allows it without penalty.
Substantially, if the extra goes to principal. Every dollar taken off the balance stops accruing interest for the remainder of the term, which is why early overpayments save far more than identical amounts paid later. Confirm with your lender that additional payments reduce principal rather than being held against future instalments.
Cheaper, yes — but riskier for you. Pledging an asset lowers the lender's exposure, which is reflected in the rate and the amount available. It also means default can cost you the asset. If the sum is modest and you can service it comfortably, unsecured borrowing avoids putting property on the line.
On a secured loan the lender can move to seize the collateral, and if it sells for less than the debt, you may still owe the remainder. On an unsecured loan the account is typically passed to a collection agency. Either way the default is recorded on your credit file and affects borrowing for years. Contact the lender before missing a payment — restructuring is far easier to arrange in advance.
The maths is exact for the terms you enter, but real agreements often carry origination fees, insurance requirements, or charges rolled into the balance. Use the result to compare structures and understand the cost of borrowing, then rely on the lender's written offer for the final numbers.
Use the amortised calculation for anything with regular instalments — mortgages, car finance, student and personal loans. Use the deferred calculation when the entire balance is due in a single payment at the end. Use the bond calculation only when the repayment figure is fixed in advance and you need to know its present value.