CasviaCasvia / Financial Planning Library
UK Financial Calculators
A structured library of UK-focused planning tools for tax, property, investing and retirement. Free to use, with assumptions and methodology shown clearly.
Savings & investing
Growth, compounding and long-term planning
UK ISA Calculator
Model ISA contributions, allowance usage and tax-free growth, including Lifetime ISA bonus assumptions.
Open tool → CalculatorUK Savings Calculator
See how regular deposits and interest build over time, with AER context and yearly results.
Open tool → Growth toolCompound Interest Calculator
Explore the effect of time, regular contributions and different compounding frequencies.
Open tool → Planning toolInvestment Return Calculator
Project long-term growth or work backwards from a target amount, including optional fees and inflation.
Open tool → Research toolUK Inflation Calculator
Compare nominal values with purchasing power and see how inflation changes money over time.
Open tool →Tax & income
2026/27 UK tax planning tools
UK Income Tax Calculator
Estimate Income Tax by band, Personal Allowance and effective rate for the current supported tax year.
Open tool → CalculatorUK Salary Calculator
Move from gross pay to estimated take-home pay using Income Tax and employee National Insurance.
Open tool → CalculatorNational Insurance
Estimate Class 1 employee National Insurance using current supported thresholds and rates.
Open tool → CalculatorCapital Gains Tax Calculator
Estimate Capital Gains Tax on shares and other assets using applicable allowances and tax bands.
Open tool → CalculatorDividend Tax Calculator
Estimate tax on dividend income after the dividend allowance and across the relevant tax bands.
Open tool → CalculatorStudent Loan Calculator
Model repayment plans, thresholds and deductions alongside earnings.
Open tool → CalculatorChild Benefit Charge
Estimate the High Income Child Benefit Charge and the resulting net benefit.
Open tool → CalculatorSelf-Employed NI
Estimate National Insurance on self-employed profits using supported rules and thresholds.
Open tool → CalculatorInheritance Tax Calculator
Explore nil-rate bands, residence nil-rate band and an estimated estate tax position.
Open tool →Property
Borrowing, repayments and transaction costs
Mortgage Calculator
Model monthly repayments, total interest, LTV and rate or deposit sensitivity.
Open tool → Planning toolHow Much Can I Borrow?
Estimate a property budget from income, deposit and existing debts as an educational starting point.
Open tool → CalculatorMortgage Overpayment Calculator
Estimate how regular overpayments may reduce interest and shorten the mortgage term.
Open tool → CalculatorStamp Duty Calculator
Estimate property transaction tax for England and Northern Ireland using current supported rules.
Open tool → CalculatorScotland LBTT Calculator
Estimate Land and Buildings Transaction Tax on Scottish residential property purchases.
Open tool → CalculatorWales LTT Calculator
Estimate Land Transaction Tax for residential property purchases in Wales.
Open tool →Retirement
Pension growth, income targets and long-term funding