Deposit, price and loan: any two give the third
There are three ways to ask the deposit question and this page takes all three. From a price and a percentage you get the cash needed. From a price and the cash you have you get the percentage. From the cash you have and the percentage you want to put down you get the price it covers, which is the direction house hunting actually starts from.
Whichever way round, the deposit and the loan add up to the price exactly, and the two percentages printed are worked out from the amounts rather than from what was typed. A page cannot show you a loan-to-value that disagrees with its own figures.
Loan-to-value is the number lenders price on
Loan-to-value is the loan as a share of the price, the mirror of the deposit share. It matters because it is the axis lenders set rates on, usually in bands rather than smoothly. Falling on the wrong side of a band by a small amount can cost more over the life of the loan than the extra deposit would have.
This is why the page prints the gap to a deposit you are aiming at. Being two thousand short of a band is a different problem from being fifty thousand short, and only one of them is worth delaying a purchase over.
Why a fifth is the usual target, and what that does and does not mean
Twenty per cent down is the line conventional lenders in the United States draw for requiring mortgage insurance. That line is their convention, not a rule of law. What the law does fix, for covered residential mortgages there, is when such insurance has to end, and it fixes it in two ways that fall on different dates. Both of those dates are arithmetic on a repayment schedule, which is why they belong to the mortgage calculator and not here: that page works them out from the loan you actually have, and the statute behind them is linked from it.
Elsewhere the number is different and the mechanism often is too. Several European markets price in bands without any separate insurance product at all. The target field takes whatever figure applies to you, and if a minimum deposit has been quoted to you, that is the figure to put in it.
The deposit is not the only cash you need
Closing costs, legal fees, survey, transfer or stamp taxes and moving costs all sit on top of the deposit, and in some markets they add several per cent of the price. None of them are in the figures here.
Nor is the reserve a lender wants to see you keep after completion, nor the first year of maintenance on a building you have just bought. A deposit that leaves nothing behind it is a deposit that turns the first repair into a credit card balance.