TrefidInput Method Result
Calculator directory

All Trefid calculators

Choose a calculator for everyday maths, household energy, driving costs, contractor tax, student loan repayments, or mortgage overpayments. Solar, EV, mortgage, and contractor tools also include private saved scenarios and copyable result receipts.

Find the right tool

Use this page when you know the type of estimate you need but not the exact calculator name. Each tool is designed for a specific question, with clear inputs and notes about what the result includes.

  • Everyday calculationsUse the main 3-in-1 calculator for arithmetic, date differences, and percentage checks.
  • Household and transport costsUse the energy calculators when you have your own tariff, appliance, mileage, or installation figures.
  • Money and tax estimatesUse the student loan, mortgage, and contractor tools for scenario planning, then check important figures against official documents.
  • Private comparisonsOn scenario-ready pages, save up to three estimates in your browser and compare them without creating an account.
Everyday maths

3-in-1 calculator

Arithmetic, date differences, and percentage calculations in one page.

Best for
Quick sums, date spans, percentage-of checks, and percentage-change checks.
Not included
Scientific functions, saved history, graphing, or professional deadline advice.
Open calculator
Solar return

Solar panel return calculator

Estimate annual solar benefit, export income, simple payback, and a long-term return figure.

Best for
Testing installer quotes, export rates, self-use assumptions, and maintenance allowances.
Extra tool
Save quote and tariff scenarios, then copy a receipt showing the generation method.
Not included
Battery modelling, finance costs, future tariff changes, panel degradation, or shading survey results.
Open calculator
Driving costs

Electric car vs petrol calculator

Compare annual EV charging cost with petrol fuel cost using mileage, efficiency, and prices.

Best for
Energy-only comparisons using your real mileage, charging rate, MPG, and petrol price.
Extra tool
Compare saved mileage, charging, and petrol-price scenarios on the same page.
Not included
Purchase price, depreciation, insurance, servicing, tax, finance, or charging losses.
Open calculator
Kitchen energy

Air fryer vs oven calculator

Compare electricity costs per cook, per week, and per year for an air fryer and electric oven.

Best for
Small appliance comparisons using appliance wattage, cooking time, weekly use, and tariff price.
Not included
Gas ovens, food quality, exact thermostat cycling, standing charges, or preheat unless you add it to time.
Open calculator
Contractor tax

UK contractor tax calculator

Estimate limited company contractor take-home pay using salary, expenses, Corporation Tax, dividends, and National Insurance.

Best for
Outside-IR35 limited company scenario planning using annual company income and extraction assumptions.
Extra tool
Save salary, income, expense, and pension scenarios privately in your browser.
Not included
VAT, Scotland bands, IR35 status decisions, benefits in kind, loans, associated companies, or accountancy advice.
Open calculator
Student loans

Student loan repayment calculator

Estimate annual, monthly, and weekly UK student loan deductions for Plan 1, Plan 2, Plan 4, Plan 5, and postgraduate loans.

Best for
Checking income-based repayment estimates against salary, bonus income, and repayment plan.
Not included
Loan interest, outstanding balance, write-off date, refunds, voluntary repayments, or payroll timing differences.
Open calculator
Mortgage planning

Mortgage overpayment calculator

Estimate interest saved and time saved from monthly and one-off overpayments on a repayment mortgage.

Best for
Testing overpayment scenarios against your balance, remaining term, and current interest rate.
Extra tool
Save monthly and lump-sum overpayment scenarios, then compare interest and time saved.
Not included
Interest-only loans, rate changes, early repayment charges, lender recalculations, remortgaging, or fees.
Open calculator

Why Trefid is different

Trefid calculators are not just answer boxes. The larger tools show a receipt, explain the calculation method, highlight the inputs that move the result most, and let you save a few scenarios locally for comparison.

That makes the result easier to audit: you can see what changed, copy the summary, and keep the calculation private on your own device.