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.

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