Loan vs value calculator

Why the two curves cross late

A loan balance falls slowly at first, because early payments are mostly interest. Value falls fastest at first, because that is how depreciation works — the steepest drop happens in the first year or two.

So the two move in opposite shapes at exactly the wrong time. The gap between them opens early, and closes only once enough principal has come off.

What being underwater actually costs

While the balance is above the value, you do not really own the thing — you owe more than it could be sold for. That has practical consequences, not just conceptual ones:

• You cannot sell without writing a check. Changing your mind means covering the difference in cash.
• A write-off leaves a balance. If it is totaled or stolen, insurance generally pays roughly what it was worth, not what you owe. The rest is still yours to pay.
• Rolling it into the next loan compounds it. Trading in while underwater usually means adding the shortfall to the next loan — starting the next one already behind.

The payment illusion

Stretching a loan lowers the monthly number, which is the number people compare. It does not lower the cost — it raises it, because interest accrues on a larger balance for longer.

The table above shows the same purchase at every term. Watch the monthly figure fall while the interest column climbs and the underwater period stretches. Those three move together, and only one of them gets quoted in the showroom.

What shortens the underwater window

Three things, in rough order of effect:

• A shorter term. The single biggest lever. Principal comes off faster than value does.
• A larger down payment. Starting with equity means the gap may never open at all.
• Buying something that depreciates less, or buying it a few years old so the steepest part of the curve has already happened to someone else.

What this model simplifies

Depreciation is treated as a steady percentage, which is a rough approximation of a curve that varies by model, mileage, condition and year. Rates differ enormously — look up real listings for the same thing a few years older rather than trusting a default here.

It also ignores taxes and fees rolled into the loan, insurance, maintenance, and any gap coverage you might hold. The aim is to show the shape of the problem, not to price your specific purchase.