Plain spreadsheets for real UK money decisions

HonestSums started with one question: how much does overpaying the mortgage by £100 a month actually save?

The online calculators gave different answers and none showed the working. So I built a sheet that did, with the maths laid out where you can see it and check it.

That is the rule for everything here. Each calculator follows the published UK rules for the current tax year, states the date those rules were checked, and ships with a Checks tab that proves the figures against worked examples. Yellow cells are yours; everything else is done for you.

The sheets cover the decisions most of us face a few times in life: taking a new job, overpaying a mortgage, buying a rental, paying for childcare, settling an estate, keeping a side hustle straight with HMRC. They are planning tools, not advice, and the tax-year sheets are updated every April when the rules change.

I design the workbooks with AI assistance and test every one in Excel before it is listed. The free calculators on this site use the same rates and the same maths as the spreadsheets.

Questions

Will the spreadsheets work in Google Sheets?

Yes. Every download includes a PDF with a "make a copy" link to the Google Sheets version, or you can import the .xlsx yourself. Formulas are chosen to work in both, and in Excel 2010 or later on Windows or Mac. No macros, no add-ins.

Is this tax advice?

No. The calculators and spreadsheets are planning tools that follow the published GOV.UK rules on the date shown. For decisions that matter, check GOV.UK or speak to a professional.

What happens when the tax year changes?

The tax-year products are updated every April. If you bought one, you can download the new version free from your purchases.

Something looks wrong

If a figure ever looks wrong, email [email protected] and I will check it and fix it.

Niall, England