There are normally three key factors that define different kinds of loans, these factors affect the risk that the lender takes on and so the interest rate. The interest rate on any loan is linked to market interest rates; the lender shouldn't be able to receive a higher rate of interest for lending the money at no risk, and the level of risk that the lender believes the borrower to have.
The three features of a particular loan are:
- whether the loan amortises or not
- whether the loan is secured or not
- whether the borrower has a guarantor on the loan
These reduce the risk of complete or total non-payment (default) of the principal or any missed interest payments. Taken in order:
Here some of the monthly payment pays a proportion of the underlying principal of the loan. This reduces the amount outstanding and so reduces the capacity for default on the full principal as part of the principal has already been paid.
In a secured loan there is an asset such as a car, house, boat, gold, shares etc. that has a value on resale that is held against the loan. The lender may repossess the security if the borrower defaults and recover their money that way. This also acts as a "stick" using the loss of property to convince the borrower that it is better to keep paying the interest. The future value of the security will be taken into account when deciding how much this reduces the interest rate.
A guarantor to a loan guarantees that the borrower will repay the loan and interest in full and, if the borrower does not fulfil that obligation, the lender is able to seek legal redress from the guarantor for the borrower's debts.
Each of these reduce the risk of the loan as detailed and so reduce the interest rate.
The interest rate, then, is made up of three parts; the market interest rate (m) plus the interest rate premium for the borrower's own credit worthiness (c) minus the value of the features of the loan that help to reduce risk (l). The interest rate of the loan (r) is categorised as: r = m + c - l.
Credit ratings themselves are an inexact science and even when two lenders are looking at the same credit score for the same person they will give a different interest rate premium. This is mostly for business reasons, and the shape of their loan book, that are too tedious to go through here.
All in all the different types of loan give flexibility at the cost of a different interest rate. If you don't want the chance of your car being repossessed you don't take a secured loan, if you have a family member who can help and doesn't mind taking on your risk take a guaranteed loan.