Mortgages and property

Almost every property decision is really two questions that have been welded into one, and separating them is most of the work. The first is whether you can carry it: the payment, the bills, the maintenance, month by month, without the current account going under. The second is whether it makes you better off: equity built, interest paid, what the money would have done elsewhere.

Those two answers routinely disagree. Upsizing usually improves net worth over ten years and makes the monthly picture tighter for three or four. Overpaying the mortgage improves net worth and takes money somewhere you cannot reach it. Buy-to-let can show a healthy paper return on a property that costs you cash every month. A calculator answers one of the two questions, which is why a calculator is a starting point rather than a decision.

That is the reason cashflow and net worth are separate statements rather than one score, and it is worth five minutes before the guides below: cashflow forecast against profit and loss explains why a household can be comfortably profitable and still short in March.

Each of these takes one question, works it through with real UK figures, and says plainly where the numbers stop being able to help. They are written to be read on their own, in any order.

Every calculator here is free, needs no account, and runs entirely in your browser. Each answers one question exactly, which is what makes them useful before a conversation with a broker and insufficient on their own.

A mortgage decision does not happen in a quiet year. It lands in the same twelve months as a nursery place, a car that needs replacing, a fix ending, and a pay rise that is smaller after tax than it looked. The reason to model rather than calculate is that those things interact, and the interaction is where households get caught out.

CrestCast forecasts a whole household ten years ahead from figures you enter: both incomes, the bills, every debt amortising on its real schedule, and the savings. Three of its surfaces do most of the work on a property decision.

Dated changes are how a move gets into the model at all. A property sold in March, a new mortgage starting in April, a deposit leaving savings the week before and the council tax going up on the same date are five separate dated entries, and the forecast obeys every one of them on the day rather than smearing them across a year.

Comparing two versions is what turns that into an answer. Save the household as it stands, save it again with the move in, and read the two side by side: cashflow, profit and loss and net worth, at one year, five and ten. The question stops being whether the bigger house is affordable and becomes what it costs you and for how long.

The forecast balance sheet is where the second of the two questions gets settled. Every mortgage and loan amortises on its own schedule, the property sits at whatever growth rate you told it, and you can read the equity at a date years out rather than inferring it. Real terms is on by default, so the figures are in today's money unless you turn that off.

There is no bank connection anywhere in CrestCast, so the balances and the payment dates are ones you enter and update. The reasoning is here, and the short version is that a feed shows you the past and a property decision is entirely about things that have not happened yet.