Methodology

Every calculation MoneyLens makes, explained in plain English — what it works out, how it gets there, and where the maths comes from.

MoneyLens provides educational calculations and estimates. It does not provide regulated financial, mortgage, credit, tax or investment advice.

Results depend on the information and assumptions entered by the user. Confirm important decisions with an appropriately authorised professional.

Debts

Payoff time at your current monthly payment

How long it takes to clear a balance if you keep paying the same amount every month. Interest is added each month at your APR divided by twelve, so the calculation accounts for interest building on whatever is still outstanding as you pay it down — which is why it takes longer than simply dividing the balance by the payment. The answer is rounded up to the next whole month. If you haven't entered an APR, it does divide the balance by your monthly payment, with no interest assumed.

Source: Standard reducing-balance (amortizing loan) maths — Wikipedia
Effective: 2026-09-23
Last verified: 2026-09-23

Debts

Required monthly payment to hit a target payoff time

The same calculation run backwards. You say how many months you want to be clear of the debt in, and this works out what you'd have to pay each month to get there, again with interest added monthly at your APR. Without an APR entered, it simply spreads the balance evenly across the months you've chosen.

Source: Standard reducing-balance (amortizing loan) maths, solved for the payment — Wikipedia
Effective: 2026-09-23
Last verified: 2026-09-23

Debts

Credit utilization

How much of a credit limit you're currently using — the balance measured against the limit. Shown only for credit cards and buy-now-pay-later, where a limit is a meaningful number; a loan or car finance agreement doesn't have one. This is not a credit score.

Source: MoneyLens' own calculation from the figures you enter
Effective: 2026-09-23
Last verified: 2026-09-23

Debts

Whether your debt payments look comfortable or worth reviewing

The share of your monthly take-home pay that goes out on debt repayments. Under 15% is described as comfortable, 15% to 35% as manageable but worth watching, and above 35% as worth reviewing. Those bands are a widely-used budgeting rule of thumb rather than anything official — they are not a credit score, and not a lending decision.

Source: MoneyLens' own calculation; the bands are a common rule of thumb, not a single external standard
Effective: 2026-09-23
Last verified: 2026-09-23

Expenses

Your essential and discretionary totals

Every expense you list is first converted to a monthly figure — anything you marked as annual is divided by twelve — and then added into one of two totals depending on the category you chose for it. Rent and groceries land in essentials; subscriptions and eating out land in discretionary.

Source: MoneyLens' own calculation from the figures you enter
Effective: 2026-09-23
Last verified: 2026-09-23

Budget

Where a month's income went

Your take-home pay for the month, with essential spending, discretionary spending, debt payments and this month's savings contribution each taken off it. Whatever remains is shown as unallocated. This uses the amount you set aside this month — never your total savings balance, which is a separate figure and would make it look as though you'd spent your entire pot in one month.

Source: MoneyLens' own calculation from the figures you enter
Effective: 2026-09-23
Last verified: 2026-09-23

Budget

Savings rate

What you set aside this month, as a share of your monthly take-home pay. Set aside £250 out of £2,500 and your savings rate is 10%.

Source: MoneyLens' own calculation from the figures you enter
Effective: 2026-09-23
Last verified: 2026-09-23

Budget

Emergency-fund runway

How many months your current savings would cover your essential spending for, if your income stopped tomorrow — your savings balance measured against essential monthly expenses only, since discretionary spending is what you'd cut first. Many guides suggest aiming for three to six months.

Source: MoneyLens' own calculation from the figures you enter
Effective: 2026-09-23
Last verified: 2026-09-23

HomeReady

Stamp duty on the purchase (England & Northern Ireland)

Stamp Duty Land Tax is charged in slices: nothing on the first £125,000, 2% on the part between £125,000 and £250,000, 5% between £250,000 and £925,000, 10% between £925,000 and £1.5 million, and 12% above that. Each rate applies only to the portion of the price inside its band, never to the whole price. First-time buyers pay nothing up to £300,000 and 5% between £300,000 and £500,000 — but that relief disappears completely above £500,000, at which point the standard rates apply to the whole purchase. An additional property (a second home or buy-to-let) adds 5 percentage points to every band — but only where the price is £40,000 or more; below that the higher rates don't apply at all. This is an estimate of the headline charge for budgeting; it doesn't model the non-resident surcharge, linked transactions, mixed use or company purchases.

Source: GOV.UK — Stamp Duty Land Tax: residential property rates
Effective: 2025-04-01
Last verified: 2026-09-24

HomeReady

Stamp duty on the purchase (Scotland)

Scotland charges Land and Buildings Transaction Tax instead, in the same slice-by-slice way: nothing up to £145,000, 2% to £250,000, 5% to £325,000, 10% to £750,000 and 12% above that. First-time buyer relief raises the nil-rate band to £175,000, worth up to £600. Buying an additional property adds the Additional Dwelling Supplement, which — unlike the English surcharge — is a flat 8% of the entire purchase price charged on top of the ordinary tax. It applies only from £40,000 upwards.

Source: Revenue Scotland — LBTT residential property rates and the Additional Dwelling Supplement
Effective: 2024-12-05
Last verified: 2026-09-24

HomeReady

Stamp duty on the purchase (Wales)

Wales charges Land Transaction Tax: nothing up to £225,000, 6% to £400,000, 7.5% to £750,000, 10% to £1.5 million and 12% above that. Wales has no first-time buyer relief at all, so ticking that box changes nothing there — the app says so rather than quietly ignoring it. Additional properties don't get a surcharge added to those bands; they use an entirely separate higher-rate table, starting at 5% and rising to 17% — and, as elsewhere in the UK, only from £40,000 upwards.

Source: Welsh Government — Land Transaction Tax rates and bands
Effective: 2024-12-11
Last verified: 2026-09-24

HomeReady

Cash you'd need on completion

The deposit, plus the purchase tax for your nation, plus whatever you've estimated for solicitor, survey, lender fees and removals. The point of adding them together is that the tax and fees can't come out of the deposit — they're extra cash on top — which is the single most common surprise for a first purchase. If the total exceeds the deposit you've entered, the shortfall is also shown as a number of months at whatever you're currently setting aside each month.

Source: MoneyLens' own calculation from the figures you enter
Effective: 2026-09-24
Last verified: 2026-09-24

HomeReady

Monthly mortgage payment and total interest

The constant monthly amount that clears the loan over the term you've chosen, with interest compounding monthly at the rate you entered — the same standard repayment-mortgage maths used for the Debts calculator. Total interest is every payment over the full term added up, minus the amount borrowed. It assumes the rate you entered applies for the whole term, which in practice it won't: most UK mortgages fix for two to five years and then move onto something else, which is what the rate-rise section is for.

Source: Standard reducing-balance (amortizing loan) maths — Wikipedia
Effective: 2026-09-24
Last verified: 2026-09-24

HomeReady

If rates rose

The same loan and the same remaining term, recalculated at 2 and 3 percentage points above the rate you entered. It's there because a fixed rate ending is a scheduled event, not a risk — the question isn't whether the rate changes but whether the payment is still affordable when it does.

Source: MoneyLens' own calculation from the figures you enter
Effective: 2026-09-24
Last verified: 2026-09-24

HomeReady

How the mortgage sits against your income

Three descriptive figures: the monthly payment as a share of your take-home pay, the loan as a multiple of a year's take-home pay, and what's left each month once the mortgage and your essential spending are both paid. The multiple is measured against take-home pay because that's the figure MoneyLens holds — lenders work from gross pay, so the multiple they quote for the same loan will be a smaller number. None of this is a lending decision: a lender also assesses credit history, employment type, existing commitments and their own stress tests, none of which MoneyLens sees.

Source: MoneyLens' own calculation from the figures you enter
Effective: 2026-09-24
Last verified: 2026-09-24

SoloMoney

Income tax on your self-employment profit

Tax is charged on profit — income minus allowable expenses — not on what you invoice. The first £12,570 is covered by the personal allowance. What's left is your taxable income, and the bands are fixed widths of it: the next £37,700 at 20%, then 40% up to £125,140 of taxable income, then 45%. Those widths matter above £100,000, where the allowance shrinks by £1 for every £2 of income and is gone entirely by £125,140 — the 20% band does NOT stretch down to fill the gap it leaves. That's why income between £100,000 and £125,140 is effectively taxed at 60%: 40p in tax, plus another 20p from the allowance you lose. (Commonly-quoted figures like "20% from £12,571 to £50,270" assume a full allowance, which is why they stop describing reality once it starts tapering.) Separately, if you also have a salary, your profit stacks on top of it rather than starting again from zero, so it's taxed at your highest rate — the single most common reason a set-aside estimate turns out far too low.

Source: GOV.UK — Income Tax rates and Personal Allowances (2026/27)
Effective: 2026-04-06
Last verified: 2026-09-24

SoloMoney

Income tax if you pay it in Scotland

Scotland sets its own bands on earned income, and there are six of them rather than three. After the same £12,570 personal allowance, the bands are again fixed widths of taxable income: the first £3,967 at 19%, then 20% to £16,956, 21% to £31,092, 42% to £62,430, 45% to £125,140, and 48% above that. Published as total-income figures those same bands read £16,537, £29,526, £43,662 and £75,000 — the difference being the allowance, which is why the published version stops holding above £100,000 as the allowance tapers away. National Insurance is not devolved, so Class 4 is identical wherever in the UK you are.

Source: GOV.UK — Income Tax in Scotland (2026/27)
Effective: 2026-04-06
Last verified: 2026-09-24

SoloMoney

National Insurance on your profit

Class 4 is charged on profit at 6% between £12,570 and £50,270, then 2% on anything above — note the rate falls rather than rises at the top. It's charged on your self-employment profit alone, not on any salary. Class 2 no longer costs anything if your profit is £7,105 or more: it's treated as paid, so the year still counts towards your State Pension. Below that it becomes optional at £3.65 a week, which the app flags as a choice rather than adding to your bill.

Source: GOV.UK — Self-employed National Insurance rates (2026/27)
Effective: 2026-04-06
Last verified: 2026-09-24

SoloMoney

What to put aside from each invoice

Your total tax and National Insurance as a share of your profit, rounded up to the next whole pound per £100 invoiced, and also shown as a monthly figure for a standing order. It rounds up deliberately: setting aside slightly too much costs you nothing, and setting aside too little is the whole problem this is meant to prevent.

Source: MoneyLens' own calculation from the figures you enter
Effective: 2026-09-24
Last verified: 2026-09-24

SoloMoney

When the bill is actually due

If last year's bill was £1,000 or more, HMRC collects next year's tax in advance as two instalments, due 31 January and 31 July. Each instalment is half of the bill for the year just assessed — so the two you pay across this year were set by last year's bill, and the two that follow are half of this year's. January is where both meet: it settles the balance still owed for the year just ended (that year's bill, less the two instalments already paid toward it) and takes the first instalment toward the next year at the same time. That combined figure is what the app shows, because it's the one people aren't ready for — and note that if your income grew, the instalments going forward grow with it. If income fell far enough, the balance can be negative and January is a refund instead. Payments on account also don't apply if more than 80% of last year's tax was collected at source, typically through a tax code; MoneyLens can't see how your tax was collected, so it doesn't assume either way.

Source: GOV.UK — Understand your Self Assessment tax bill: payments on account
Effective: 2026-09-24
Last verified: 2026-09-24

SoloMoney

What this deliberately doesn't cover

An estimate for planning, not a tax return. It doesn't model dividends or savings income (which have their own rates and allowances), the £1,000 trading allowance, pension contributions or Gift Aid extending your basic-rate band, capital allowances, losses carried forward, student loan repayments, the annual maximum where someone pays both Class 1 and Class 4, or VAT. Each of those would need its own care, and a confidently wrong number is worse than a stated gap — so they're named here rather than silently omitted.

Source: MoneyLens' own scope statement
Effective: 2026-09-24
Last verified: 2026-09-24

Savings

Current savings, when you've itemized your accounts

If you've listed your accounts separately — cash savings, a Stocks & Shares ISA, a general investment account and so on — your Current savings figure is the total of those balances, and updates whenever you change one. If you haven't itemized, it's simply the single figure you typed in. Both are equally valid; itemizing is optional.

Source: MoneyLens' own calculation from the figures you enter
Effective: 2026-09-23
Last verified: 2026-09-23

Savings

Adding a month's contribution to your balance

Only when you press the button — never automatically. It adds this month's savings contribution to your Current savings balance, and won't do it twice in the same calendar month. It stays manual on purpose: your real balance also moves with interest, withdrawals and deposits made elsewhere, so a figure that updated itself every month would quietly drift away from your actual bank balance.

Source: MoneyLens' own calculation from the figures you enter
Effective: 2026-09-23
Last verified: 2026-09-23