Practical calculators with their assumptions explained
Use Attach Planet tools to organise figures, test an assumption and prepare better questions. Every published tool should explain what it calculates, what it leaves out and when the result needs to be checked with a provider or qualified professional.
Available now
Tools are published only after the calculation, validation, wording and page-level explanation have been checked. This means the library will grow more slowly, but each live calculator should be understandable without hidden assumptions or a sales form.
Compare estimated monthly payments for a current and proposed mortgage using capital repayment, interest-only or part-and-part figures.
Repayment, affordability, deposit and buy-to-let tools are being reviewed before dedicated public pages are published.
Rental-yield and property-tax tools require current assumptions, clear jurisdiction labels and testing before they are made public.
How to use an online calculator responsibly
- Read the scope: Confirm the country, date, calculation type and purpose of the tool.
- Use accurate inputs: Enter figures from current documents rather than rounded estimates where the decision matters.
- Check exclusions: Identify fees, taxes, charges, incentives, future changes and personal circumstances not included.
- Test scenarios: Change uncertain figures to understand how sensitive the result is to rates, costs or timescales.
- Keep the result in context: A calculation may show a numerical difference without deciding suitability or affordability.
- Verify before acting: Check material figures with the relevant provider, official source or qualified professional.
What a trustworthy tool page should show
Attach Planet tool pages state the inputs, method, assumptions, rounding, limitations and review date. Results are provided before any request for personal details, and calculator code is loaded only on pages that use it.
Where a result concerns finance, property, tax, law or another high-stakes area, the page should link to relevant independent guidance and explain when professional advice may be appropriate.
A calculator result depends on the information entered and the method stated. Providers may use different assumptions, eligibility rules, rounding or fees. Attach Planet tools do not approve applications, predict offers or provide personal financial, legal, tax or investment advice.
Calculator and tool FAQs
Are Attach Planet calculators free to use?
Yes. The currently published calculator can be used without entering contact details. If this changes for a future tool, the purpose and data use will be explained clearly.
Why are some calculators not yet available?
Legacy calculators are being reviewed for calculation accuracy, validation, accessibility, current assumptions and clear explanation pages before they are made public.
Can a calculator tell me whether a product is suitable?
No. A calculator can estimate a result from selected inputs. It cannot assess all personal circumstances, eligibility criteria, contract terms, risks or professional obligations.
How can I report a calculator problem?
Use the Contact page and include the tool, figures entered, expected result and what happened. Do not send passwords, full account numbers or other unnecessary sensitive information.
