Every calculator you actually use,
in one place
Percentages, VAT, mortgages, loans and bill splitting - answered in seconds, with the workings shown so you can trust the number. Free, no signup, and nothing you type ever leaves your browser.
Everyday maths
Percentage Calculator
What is X% of Y, reverse percentages and percentage change - with the workings shown.
Open calculator →Discount Calculator
Sale price, money saved, and what stacked "extra % off" deals really cost.
Open calculator →Tip Calculator
Tip, total and per-person share when you split the bill - no awkward maths at the table.
Open calculator →Tax & business
UK VAT Calculator
Add or remove VAT at 20%, 5% or a custom rate, with a full net / VAT / gross breakdown.
Open calculator →Reverse VAT Calculator
Start from a gross price - or just the VAT amount - and work back to the net figure.
Open calculator →Mortgages & loans
Mortgage Repayment Calculator
Monthly payments, total interest and the true cost of fees on repayment or interest-only deals.
Open calculator →Mortgage Overpayment Calculator
How much interest and time a monthly or lump-sum overpayment really saves you.
Open calculator →How Much Can I Borrow?
A realistic borrowing estimate from your income, deposit and outgoings.
Open calculator →Loan Repayment Calculator
Monthly repayments and total interest on personal loans and car finance.
Open calculator →Why another calculator site?
Because most of them are either buried under adverts, oddly slow for something that's doing school-level arithmetic, or vague about how they got their answer. Zhaku takes the opposite approach: every tool loads instantly, works beautifully on a phone, and shows its workings underneath the result, so you can sanity-check the maths yourself or repeat it on the back of an envelope.
The nine calculators here cover the questions we found ourselves googling again and again - what's 20% off this, how much VAT is in that invoice, what would this mortgage actually cost per month, is it worth overpaying. Nothing exotic, just the everyday stuff done properly.
A few things we promise
- Your numbers stay yours. All calculations run in your browser. We never see the figures you type.
- UK-first. VAT rates, mortgage conventions and currency formatting all follow UK practice - though most tools work anywhere.
- Honest limitations. Where a result is an estimate (borrowing power, for instance), we say so plainly instead of pretending it's a quote. For decisions that deserve proper guidance, we point you to impartial sources like the government-backed MoneyHelper rather than a sales pitch.