A debt payoff planner for every debt a UK household has

CrestCast models a mortgage, a loan, a credit card and a student loan. Nothing else. Each of those four is modelled properly rather than approximated with a generic amortisation formula.

Mortgages can be repayment or interest only. Loans have one extra option worth calling out: an informal or family loan, with no interest and no schedule. Money you owe a parent, a sibling or a friend, paid back when you can. It is a real thing plenty of households carry and almost nothing models, and leaving it out of a forecast quietly overstates how much spare cash you have.

Where the app can work out how far through you are without inventing anything, it says so: a mortgage you entered an original amount for, or a loan entered at what you borrowed, carries a paid-so-far figure and a percentage alongside the balance, and it reads the same on the list, the analysis screen and the timeline. A credit card and a student loan get no percentage, because neither has an original to measure against and a made-up denominator is a made-up answer.

Fixed-rate expiry and reversion to the standard variable rate is modelled directly. You enter the fixed rate, the date the fix ends and the rate you would revert to, and the forecast steps the payment up on that date and carries the higher payment through every month after it. Your cashflow in 2029 reflects a decision your lender makes in 2028.

If you would rather plan on remortgaging than on reverting, there is an option that assumes exactly that, and the forecast holds the rate instead of jumping it. Tracker mortgages are entered as base rate plus a margin and resolved against the Bank of England base rate the app holds. And you can put an arbitrary rate change on any date you like: the instalment is recomputed over the remaining term from that point forward, which is what a lender does, rather than being nudged for a single month.

A credit card is not a loan with a different label, so it does not use the loan maths. It has its own simulator, including a 0% promotional period with an end date and three things that can happen when the promotion runs out: the balance reverts to the standard rate, a balloon payment clears it, or it moves to a balance transfer.

Credit utilisation, your balance against your limit, is tracked and flagged amber once it goes above 30%. The promotional end date is also flagged on the forecast charts, so the month your 0% deal expires is marked rather than being something you find out about from a statement.

Plans 1, 2, 4 and 5 are supported, along with the Postgraduate loan, each on its own threshold and rate. Plan 4 is the Scottish one. Repayment is income-contingent: a percentage of what you earn above the plan threshold, computed on gross pay after pension contributions rather than on take-home.

All five drive the repayment that comes out of your pay, set on the salary screen, and all five are on the liability form too, so a Plan 4 balance is tracked as a Plan 4 balance rather than approximated with a neighbour.

Plan 1 interest follows Bank Rate when it is the lower leg, and the Bank Rate what-if applies that to a Plan 1 loan. How the rule works, and when a cut would change the balance, is in does Bank Rate affect your student loan.

The detail that matters if you have more than one job is that your incomes are aggregated and assessed against a single threshold, not tested job by job. Two part-time roles that each sit under the threshold can still produce a repayment when they are added together, and a per-job calculation gets that wrong every time.

You can set a recurring monthly overpayment with a start date, so “an extra £250 a month from April” is a thing the forecast understands rather than something you approximate. And when a bonus lands, add a one-off overpayment on the date it arrives under Planned changes. Both are set in your inputs; tap the debt on any statement to see how its figure was worked out.

Both re-amortise the debt properly and both move the clearance date. Debt interest is also split out from capital in the profit and loss, so you can see what a debt actually costs you rather than just what leaves the account. On a mortgage in its early years, the gap between those two numbers is usually larger than people expect.

Say the mortgage is £220,000 at 4.6%, fixed until 03/2028, reverting to 7.4% after that. A car loan of £14,000 at 9.9% over five years. A credit card carrying £6,200 on 0% until 09/2027, reverting to 22.9%. A Plan 2 student loan taking its slice of everything above the threshold.

The analysis screen gives you a payoff date for each one, written as paid off in X years Y months. The charts flag the milestones: the month the card promotion ends, the month the fix expires, the month the car loan finishes and the payment stops. Your cashflow drops in 09/2027 when the card starts charging interest, drops again in 03/2028 when the mortgage payment steps up, and jumps in the month the car loan clears. Those are three separate events on three separate debts, and you see all of them in one forecast.

An amortisation schedule for one loan is a well-known spreadsheet exercise. Balance, rate, payment, a column of months. Plenty of people have built one and it works fine.

Now build four. One of them reverts to a different rate in 2028, which means recomputing the instalment over the remaining term at that boundary rather than just changing a cell. One has a promotional rate that ends, with a different behaviour depending on which of three things you do about it. One has a repayment that depends on your income after pension contributions, aggregated across two jobs. And all four have to agree with each other and with your cash balance every single month, so that when you drop a one-off overpayment into March you can see what it does to your account balance in December.

That is four schedules, a tax calculation and a running cash position, all of which have to stay in step when you change any one input. Spreadsheets do not fail at this because the maths is hard. They fail because the maintenance is endless, and because nobody rebuilds the whole thing when their circumstances change.

Debts do not sit in their own screen in CrestCast. They are part of the household forecast, so the month a loan clears you see it three ways at once: the payment leaves your cashflow, the interest leaves your profit and loss, and the liability leaves your net worth. That is the difference between knowing a debt ends and knowing what your money looks like afterwards.

It also means you can compare. Save a version with an overpayment and one without, and put them side by side on scenario comparison to see both futures against each other rather than reasoning about one at a time.

There is no snowball, and the avalanche only goes as far as your credit cards: the Clear debt first preset sorts those by rate and puts your loans in beneath them, and mortgages stay out of it. Nothing ranks every debt you own and tells you which to attack. You set the order, and the forecast shows you what it does.

The student loan write-off date is a date you type in yourself: nothing derives it from your plan, and if you leave it blank the loan never writes off in the forecast.

An overdraft has no facility of its own to set up with a limit and a rate, though an account you take into the red is shown as a debt rather than as a negative balance. Car finance goes in as an ordinary loan: there is no PCP or hire purchase structure, so no guaranteed future value, no optional final payment and no mileage, and the balloon option lives on credit cards rather than on loans.

And CrestCast does not connect to your bank. Balances are yours to enter and yours to keep current: a few minutes a month, in exchange for a forecast with no credential shared and nothing about your debts read from anywhere. here is why I built it that way.