Personal finance & small business hub
Calculators & tools, that just work.
A growing collection of free online calculators for personal finance and small business — mortgages, salary, FIRE, ROAS, burn rate and more. No sign-up, no clutter, just clear answers in your browser.
About
Practical math for personal finance & small business.
Websums is a hub of free calculators for the everyday money questions individuals and small business owners actually face — mortgages, take-home pay, retirement timelines, ad spend returns, runway, unit economics. Most online calculators are slow, ad-stuffed, or hidden behind sign-ups; we're building fast, focused tools that give you the answer quickly and stay out of the way.
Every calculator runs in your browser. Nothing you enter leaves your device. New tools are added regularly.
Tools
Available calculators
Pick a calculator below. New tools are added regularly — check back soon.
Mortgage Calculator
Estimate your monthly mortgage payment, total interest, and amortisation across the loan term.
Open tool →Stamp Duty (UK)
Work out exactly how much SDLT you'll pay — first-time buyer relief, home mover, or additional-property surcharge.
Open tool →Rent vs. Buy
Compare the true total cost of renting vs buying — including maintenance and the opportunity cost of your deposit.
Open tool →Salary Calculator
Work out your take-home pay after UK Income Tax and National Insurance — monthly, weekly, daily.
Open tool →Corporation Tax (UK)
Turnover in, tax bill out. Marginal relief, effective rate, and net profit for UK limited companies.
Open tool →Compound Interest
Visualise long-term investment growth with regular contributions and compound interest. Year-by-year chart.
Open tool →Loan Repayment
See exactly how each payment splits between interest and principal over the life of any loan.
Open tool →Inflation Impact
See what your money today will be worth in 5, 10, or 20 years — and how much you'd need just to keep up.
Open tool →Subscription Leak Finder
Add up your monthly subscriptions to see the real annual drain — and what that money could be worth invested.
Open tool →ROAS Calculator
Return on ad spend, break-even ROAS, and true profit per click — see whether your campaigns actually make money.
Open tool →Remote Work Savings
Fuel, transit, lunches, coffee, car wear — see how much money and time you save by skipping the commute.
Open tool →Side Hustle ROI
Work out the real hourly rate of a freelance project after tax, expenses, and the unpaid hours nobody quotes for.
Open tool →Burn Rate & Runway
How long until the cash runs out? Net burn, gross burn, runway in months, and whether you're default-alive.
Open tool →Unit Economics
True profit per unit after platform fees, shipping, ad spend, and returns. Amazon, Shopify, eBay, Etsy presets.
Open tool →Bulk Discount Pricing
Set volume price breaks and see margin at every tier. Stop discounting blind — price an order in seconds.
Open tool →Time to Freedom (FIRE)
Find the exact age you can stop working. Your FI number, savings rate, and the years between you and freedom.
Open tool →Travel Budget Estimator
Pick a destination, days, and style — get a realistic breakdown of flights, hotels, food, transit and activities.
Open tool →More coming soon
Percentage, unit conversion, savings goal, currency, and more — in development.
Coming soonWhy Websums
Built to be simple
No sign-up walls, no spinners, no hidden fees.
100% free
Every calculator is free to use. No subscriptions, no paywalls.
Privacy first
Calculations happen in your browser. We never store the numbers you enter.
Works anywhere
Mobile, tablet, desktop — fast and responsive on any device.
Always growing
New tools added regularly. Got a request? Let us know.
Contact
Got an idea? Get in touch.
Suggestions, feedback, or a calculator you'd like us to build — drop us a line.
hello@websums.com