Loan to value and downpayments

Upon making a mortgage loan for the purchase of a property, lenders usually require that the borrower make a downpayment; that is, contribute a portion of the cost of the property. This downpayment may be expressed as a portion of the value of the property (see below for a definition of this term). The loan to value ratio (or LTV) is the size of the loan against the value of the property. Therefore, a mortgage loan in which the purchaser has made a downpayment of 20% has a loan to value ratio of 80%. For loans made against properties that the borrower already owns, the loan to value ratio will be imputed against the estimated value of the property.
The loan to value ratio is considered an important indicator of the riskiness of a mortgage loan: the higher the LTV, the higher the risk that the value of the property (in case of foreclosure) will be insufficient to cover the remaining principal of the loan.

Value: appraised, estimated, and actual

Since the value of the property is an important factor in understanding the risk of the loan, determining the value is a key factor in mortgage lending. The value may be determined in various ways, but the most common are:

1. Actual or transaction value: this is usually taken to be the purchase price of the property. If the property is not being purchased at the time of borrowing, this information may not be available.
2. Appraised or surveyed value: in most jurisdictions, some form of appraisal of the value by a licensed professional is common. There is often a requirement for the lender to obtain an official appraisal.
3. Estimated value: lenders or other parties may use their own internal estimates, particularly in jurisdictions where no official appraisal procedure exists, but also in some other circumstances.

Payment and debt ratios

In most countries, a number of more or less standard measures of creditworthiness may be used. Common measures include payment to income (mortgage payments as a percentage of gross or net income); debt to income (all debt payments, including mortgage payments, as a percentage of income); and various net worth measures. In many countries, credit scores are used in lieu of or to supplement these measures. There will also be requirements for documentation of the creditworthiness, such as income tax returns, pay stubs, etc; the specifics will vary from location to location.
Some lenders may also require a potential borrower have one or more months of "reserve assets" available. In other words, the borrower may be required to show the availability of enough assets to pay for the housing costs (including mortgage, taxes, etc.) for a period of time in the event of the job loss or other loss of income.
Many countries have lower requirements for certain borrowers, or "no-doc" / "low-doc" lending standards that may be acceptable in certain circumstances.

Standard or conforming mortgages

Many countries have a notion of standard or conforming mortgages that define a perceived acceptable level of risk, which may be formal or informal, and may be reinforced by laws, government intervention, or market practice. For example, a standard mortgage may be considered to be one with no more than 70-80% LTV and no more than one-third of gross income going to mortgage debt.
A standard or conforming mortgage is a key concept as it often defines whether or not the mortgage can be easily sold or securitized, or, if non-standard, may affect the price at which it may be sold. In the United States, a conforming mortgage is one which meets the established rules and procedures of the two major government-sponsored entities in the housing finance market (including some legal requirements). In contrast, lenders who decide to make nonconforming loans are exercising a higher risk tolerance and do so knowing that they face more challenge in reselling the loan. Many countries have similar concepts or agencies that define what are "standard" mortgages. Regulated lenders (such as banks) may be subject to limits or higher risk weightings for non-standard mortgages. For example, banks and mortgage brokerages in Canada face restrictions on lending more than 80% of the property value; beyond this level, mortgage insurance is generally required.^[5]