Calculators that explain
what to do next.
Mortgage, tax, salary and business calculators built for UK rules — with plain-English AI explanations of what your numbers mean.
Start with the big decisions
Six calculators people reach for most often — the rest you can browse by category below.
Mortgage payment UK
Monthly cost, total interest, amortisation schedule
Salary take-home UK
PAYE, NI, student loan and pension on your gross pay
Sole trader vs Ltd UK
Compare take-home at any income with break-even
Stamp Duty UK
SDLT in England, LTT in Wales, LBTT in Scotland
ISA vs SIPP vs GIA UK
Compare wrappers by your marginal tax rate
Salary vs dividend UK
Optimal director pay split for your Ltd company
More than just a number
Every calculator tells you what the result means and what to do next.
Your £1,548 monthly payment is in line with typical UK mortgages for a £325k property at current rates. Over 25 years you’ll pay £204,400 in interest — that’s 78% on top of what you borrowed.
Something to consider: increasing your deposit to 30% (£97,500) would drop the monthly to about £1,355 and save roughly £32,000 in interest — useful if you can hold the offer that long.
UK money in four areas
Each hub covers one side of UK money decisions with calculators that go deep on the rules.
Buying, remortgaging, overpaying, stamp duty — built for SDLT, LTT and LBTT.
- Mortgage payment
- Affordability
- Stamp Duty
- Overpayment
- Remortgage
PAYE, self-assessment, dividends, CGT, side hustle — current HMRC rules applied.
- Salary take-home
- Self-employed
- Dividend tax
- CGT
- HICBC
Sole trader vs Ltd, salary vs dividend, IR35, VAT, day rate — for UK contractors and directors.
- Sole trader vs Ltd
- Salary vs dividend
- IR35
- Flat Rate VAT
- Day rate
ISA, SIPP, LISA, GIA, compound interest, FIRE, drawdown — wrapper-aware maths.
- ISA vs SIPP vs GIA
- Compound interest
- FIRE number
- Pension drawdown
- LISA
From number to decision
Three steps. Calculation in your browser, explanation on demand.
Enter your numbers
Property price, salary, contract rate — whatever the calculator needs. UK defaults preloaded so you can start fast.
Get the result instantly
Calculated using current UK rules — HMRC bands, FCA-referenced rates, Bank of England data where relevant.
Ask AI what it means
Plain-English explanation, context against UK averages, and a suggestion for what to consider next.
About Calclens
Why Calclens exists
Most online calculators give you a number and walk away. We built Calclens because UK users making real money decisions deserve more than that — AI calculators that explain the result, reference UK rules, and suggest what to consider next. From mortgages and stamp duty to dividend tax and salary take-home, every calculator runs in your browser, explains itself in plain English, and never asks for your email. We’re building this in public, launching one calculator at a time, focused entirely on the British market.
How the AI explanation works
We use Claude — the language model from Anthropic — to explain what your number actually means. When you calculate your monthly mortgage payment, our AI calculator tells you whether it’s typical for UK properties at that price, how much you’ll pay in interest over the term, and what would happen if you increased your deposit. When you calculate your director’s salary versus dividend split, the AI walks you through the trade-offs against current HMRC bands. The number is the start of the conversation, not the end. See how the AI explanation layer works for the technical detail.
Built for UK residents, with UK rules
Every Calclens calculator uses official UK data and regulations. Our salary take-home calculator follows current HMRC PAYE bands, our stamp duty calculator reflects SDLT thresholds for England and Northern Ireland (with separate logic for LTT in Wales and LBTT in Scotland), and our mortgage tools reference Bank of England rate data. We link to primary sources for every claim and document our calculation logic openly — see our methodology and full source list.
Start with your biggest decision
Most people come here for one of these three.