About Auxitool
Auxitool exists to answer one kind of question well: the sort you would otherwise work out in a spreadsheet, on the back of an envelope, or by trusting a number someone else gave you.
Fast by design
Lightweight pages that respond as you type. No loading spinner between a number and its answer.
Built to be read
Clean layouts, legible figures, and an explanation of what the result actually means underneath every tool.
Private by default
Calculations happen in your browser, and the values you enter are not stored.
Where it came from
The site began as years of spreadsheets and small utilities built for personal use: working out whether an overpayment was worth making, what a move would actually leave behind, how a subnet should be carved up. The calculations were sound; the tools around them were held together with cell references and memory.
Auxitool is the result of rebuilding those ideas properly: the same arithmetic, made durable, readable on a phone, and explained well enough that you can check the working rather than take the answer on faith.
How the tools are built
Every calculator runs entirely in your browser, and there is no account to create. Each tool carries a written explanation of the method it uses, what it deliberately leaves out, and where its estimate is likely to differ from a real quote.
The estimators are for planning and comparison. They are general information, not financial advice, and they cannot account for anyone's particular circumstances. A qualified adviser, broker or lender can.
What's here now
The catalogue is deliberately small and grows based on what people ask for:
- Mortgage Calculator: Estimate monthly payments, interest costs, and remaining balance.
- Mortgage Overpayment Calculator: Work out how much extra to pay, and what it saves in interest and years.
- Cost of Selling a House: Itemise agent fees, conveyancing, removals and stamp duty on your next place.
- House Sale What-If: Estimate equity released, deposit, new mortgage and the cash left over.
- CIDR Calculator: Work out subnet masks, ranges, and IP counts quickly.
- CIDR Ranges: Reference table of prefixes, masks and address counts for /0 to /32.
- Epoch Converter: Turn a Unix timestamp into a date, or a date into a timestamp.
If something returns a figure that looks wrong, or you would like a tool that is not here yet, the contact page is the way to say so.