GAP Insurance Calculator
The car, the loan and the drop
Your result will appear here
Fill in the fields and this updates as you type.
Know what this estimate is based on
- Jurisdiction
- United States — insurance is regulated state by state, so the rules behind a premium are your state's, not a federal schedule
- Rules and time period
- Premiums, limits and deductibles are the figures you enter. Health plan cost-sharing caps, Medicare amounts and state filings all reset annually.
- Scope and limitations
- Educational estimate only. Rates, required coverages and available discounts differ by where you live. Your premium is set by an insurer's own underwriting — driving record, claims history, credit-based insurance score where permitted, the property itself — and only a quote is binding. What a policy pays depends on its exclusions and limits, not on this estimate.
- Source links checked
- Sep 19, 2026
Built and regression-tested by Smart Tools Lab. It has not been individually reviewed by a licensed financial, tax, or legal professional.
Primary sources
How to use
- 01
Enter the price of the car and everything you are putting against it up front — cash deposit and trade-in equity together. The difference between them is the loan every other figure on this page is measured against, and the deposit is the most powerful lever here: it is the only input that can remove the gap outright rather than merely shrink it.
- 02
Enter the APR and the length of the loan. The term matters more than the rate on this page, because stretching the term slows the rate at which the balance falls without slowing the rate at which the car loses value by a single dollar. The two lines drift apart, and the months you spend underwater are largely the months the longer term added.
- 03
Enter what GAP cover costs. Get the figure from your own auto insurer as well as from the dealer, because they are rarely the same, and the dealer's version is usually financed into the loan, so you pay the APR on it too. The page weighs that price against the largest gap the loan ever opens, which means an inflated price can turn a reasonable product into a bad one on its own.
- 04
Open Advanced options to set how fast the car loses value. The defaults of 20% in the first year and 15% in each year after are a conventional assumption rather than a forecast for your model, and the page compounds them month by month rather than dropping the value in annual steps. Run both ends of a plausible range: a vehicle that holds its value closes the gap by itself, and one that does not can hold it open for years.
- 05
Read the largest gap first, then the time underwater, then the verdict. The largest gap is the most GAP could ever have to pay, so it is the ceiling on what the cover is worth to you. The time underwater says how much of the loan is genuinely exposed — and if it reads None, no price for GAP is a good price.
Formula
The loan is the price of the car minus the deposit and trade-in, floored at zero, and the monthly payment is the ordinary amortizing payment on it: payment = principal × i ÷ (1 − (1 + i)^(−n)), where i is the APR ÷ 12 and n is the term in months. The page then walks the loan forward one month at a time — balance = balance × (1 + i) − payment, floored at zero — so the balance it shows is the real amortized figure rather than a straight line. The car's value falls on a separate curve: value at month m = price × (1 − first-year drop)^min(m ÷ 12, 1) × (1 − later drop)^max(0, m ÷ 12 − 1), which compounds the annual percentage smoothly across the months rather than stepping down once a year. The gap in any month is the balance minus the value; the page counts every month where that is positive as time underwater, and records the largest gap and the month it peaked. The verdict is a simple comparison: GAP is reported as worth buying when the largest gap exceeds the price of the cover. Note what that comparison does not do — it does not multiply by the chance of a total loss. It answers whether GAP could ever pay more than it costs, not whether it probably will.
Example
A $38,000 car with $3,000 down, financed over 72 months at 7.5%, carries a $605 monthly payment and never goes underwater at all: the largest gap is $0, the time underwater reads None, and the page reports that there is no gap to cover. The schedule shows why. At month 12 you owe $30,200 against a car worth $30,400; at month 24, $25,028 against $25,840; at month 36, $19,454 against $21,964; and the distance keeps widening to $6,975 against $15,869 at month 60. At $600, GAP on this loan would be paying for a risk the deposit already removed. Now the alternates, each named. Set the down payment to $0 and the payment rises to $657, the largest gap becomes $2,389 around month 12, and you spend 2 years and 8 months underwater — GAP is worth its price. Stretch that zero-deposit loan to 84 months and the payment falls to $583 while the largest gap climbs to $3,416 around month 17 and the time underwater reaches 4 years. Put $1,000 back in on the 84-month loan and the peak falls to $2,588 with a $568 payment. And if the car depreciates harder than the defaults assume — 25% in the first year rather than 20%, on the zero-deposit 84-month loan — the peak gap reaches $5,225 around month 14 and the loan is underwater for 4 years and 5 months.
Definitions
- Price of the car
- The amount financed before any deposit — the out-the-door figure the loan is written against, including taxes and fees if they were rolled in. The page also treats it as the car's value on day one.
- Down payment and trade-in
- Cash plus trade-in equity applied at signing. The one input that can close the gap entirely rather than merely narrow it, because it lowers the loan without touching the car's value.
- Loan APR
- The annual rate on the loan, converted to a monthly rate and applied to the outstanding balance each month. It sets how much of each early payment goes to interest rather than principal.
- Loan term
- How many months the loan runs. Longer terms lower the payment and slow the fall of the balance, which is what opens and lengthens a gap.
- Price of GAP cover
- What the cover costs, whether paid up front or financed. Financed into the loan it accrues interest at the APR, so the dealer's figure is not the price you actually pay.
- Value lost in year one
- The share of the car's value that disappears in the first twelve months. An advanced input, compounded across the months rather than applied as a single annual step.
- Value lost each year after
- The share lost in each later year, applied the same way. Together with the first-year drop it defines the whole depreciation curve the loan is measured against.
- Largest gap
- The most the balance ever exceeds the car's value over the life of the loan. The ceiling on what GAP could pay, and the figure the price of cover is compared against.
- Time underwater
- How many months of the loan the balance sits above the value. Reads None when the loan never goes underwater, which is a complete answer on its own.
- Actual cash value
- What the car was worth immediately before the loss — the basis on which a collision or comprehensive claim is settled, and the figure GAP measures the shortfall from. Not what you paid, and not what you owe.
Frequently asked questions
Do I need GAP insurance?
Not on this page's defaults, and it is worth seeing why before you look at the cases where you do. A $38,000 car with $3,000 down over 72 months at 7.5% never goes underwater: the largest gap is $0, the time underwater reads None, and the verdict line says there is no gap to cover. At month 12 you owe $30,200 against a car worth $30,400, and the balance stays below the value for the rest of the loan. The $3,000 deposit is already doing the job GAP is sold to do. Take the deposit away and the answer reverses immediately.
What happens if I put nothing down?
The gap opens the day you drive away. Keep the same $38,000 car, the same 7.5% rate and the same 72-month term but set the down payment to $0: the monthly payment rises from $605 to $657, the largest gap is $2,389 around month 12, and you are underwater for 2 years and 8 months of the loan. Against a $600 price the verdict flips to Yes, because GAP costs less than the $2,389 it would cover at the worst point. Nothing about the car changed. The whole difference is the $3,000.
Does a longer loan term make GAP more necessary?
Substantially, and this is the single most underrated part of a long auto loan. Take the zero-deposit case and stretch it from 72 months to 84: the payment falls from $657 to $583, which is exactly why long terms sell, but the largest gap climbs from $2,389 to $3,416 and it now peaks around month 17 rather than month 12. You stay underwater for 4 years of the 84-month loan, and even at month 48 you owe $18,738 on a car worth $18,669. The lower payment was bought with four years of negative equity.
What is negative equity and why does it happen at all?
It is the amount by which the loan exceeds what the car would sell for, and it happens because two curves have different shapes. A car loses a large share of its value in the first year and a smaller share each year after, so the value falls fastest at the start. A loan does the opposite: early payments are mostly interest, so the balance falls slowest at the start. Put a steep early drop against a slow early payoff and the loan can sit above the value for years, even though both are heading to the same place. The schedule on this page draws both lines so you can see where they cross.
When does GAP actually pay?
Only when the car is a total loss or is stolen and not recovered. Your collision or comprehensive coverage settles first, at the car's actual cash value on the day of the loss, and GAP pays the difference between that settlement and what you still owe. It is not payment protection: it does nothing for a job loss, an illness, a repossession or a crash the insurer decides is repairable. It also does nothing if you have no collision and comprehensive coverage in the first place, because there is no settlement for it to sit on top of.
Do I have to buy GAP from the dealer?
No, and the federal disclosure rules make the point for you. Dealer GAP is usually written as a debt cancellation agreement, and Regulation Z at 12 CFR 1026.4(d)(3) lets a creditor keep that charge out of the finance charge only if three things are true: the agreement is not required by the creditor and that fact is disclosed in writing, the fee for the initial term is disclosed in writing, and you sign or initial an affirmative written request for the coverage after receiving those disclosures. If it were required, 12 CFR 1026.4(b)(10) would fold the charge into the finance charge and the APR. So a loan presented as conditional on buying GAP is contradicted by the paperwork in front of you.