Terms of Use

Last updated: 2026-05-08

Draft — not yet legally reviewed. Standard hobbyist / open-source disclaimers + UK tax-specific carve-outs. Before public launch, review against UK consumer-rights law and have a UK solicitor sign it off.

By using this Calculator, you agree to these terms. If you don't agree, please don't use it.

1. What this Calculator is

A free, open-source UK tax estimation tool that follows the HMRC PAYE Tax Table Routines specification. It computes estimates of income tax, National Insurance, and related deductions across seven common UK tax situations: PAYE employee, Limited Company director, Umbrella contractor, IR35 (inside vs outside), Sole Trader, Dividend tax (for investors holding shares outside an ISA), and a Self Assessment estimator that combines multiple personal income streams.

2. What this Calculator is NOT

This is not financial advice. This is not tax advice. This is not legal advice.

The Calculator's output is an estimate, intended for general information and rough planning. It is not a substitute for:

Advice from a qualified UK accountant, tax adviser, or solicitor.
Your own check of HMRC's official guidance at https://www.gov.uk/.
The actual figures HMRC will assess for your specific circumstances (which depend on data we don't have, such as benefits in kind, dividends from external sources, multiple employments, capital gains, etc.).

Do not rely on this Calculator for:

Filing self-assessment returns.
Negotiating salary, day rates, or contract structures with significant financial impact.
Legal disputes, audits, or HMRC appeals.

If you need accuracy that holds up against HMRC, consult a qualified professional.

3. Accuracy

We follow the published HMRC PAYE Tax Table Routines (currently v24.0, February 2026) and seed tax-rate data from gov.uk. We test the calculation engine against HMRC's reference vectors and update annually for new tax years.

Despite this, we make no warranty that the Calculator's output is accurate, complete, or up-to-date for your specific circumstances. Tax rules change; edge cases exist; bugs happen.

If you find a calculation that disagrees with HMRC, please report it on GitHub: https://github.com/loglux/tax_calculator/issues

4. Limitation of liability

To the fullest extent allowed by UK law:

The Calculator is provided "as is" and "as available", without warranties of any kind (express or implied), including merchantability, fitness for a particular purpose, or non-infringement.
We accept no liability for any direct, indirect, incidental, consequential, or special damages arising from your use of the Calculator — including but not limited to:
Tax under-payment or over-payment based on our estimate.
Penalties or interest charged by HMRC.
Lost income from contractual decisions taken on the basis of our output.
Service downtime, data loss, or calculation errors.
Your sole remedy if dissatisfied is to stop using the Calculator.

This clause does not exclude liability for death or personal injury caused by negligence, fraud, or other liability that cannot lawfully be excluded under UK consumer law.

5. Open source licence

The Calculator's source code is published under the GNU Affero General Public License version 3 (AGPL-3.0). Full licence text: the LICENSE file in the GitHub repo.

In plain English, AGPL-3.0 means:

You are free to use, study, modify and self-host the software for personal, educational or non-commercial purposes.
If you run a modified version as a network service (e.g., host it on your own URL for other people to use), you must publish your source code under the same AGPL-3.0 licence, including any modifications. Section 13 of the licence applies.
You may not relicense the code under a less restrictive licence or build a closed-source product on top of it.

If you want to use the calculator in a commercial product without the AGPL-3.0 source-publication requirement (e.g., embed it in a closed-source SaaS, redistribute under a permissive licence to your customers), contact us via the contact form for a commercial-licence arrangement.

6. Acceptable use

Don't use the Calculator to:

Make automated requests that exceed our rate limit (60 requests per minute per IP for anonymous traffic) or otherwise abuse the service.
Attempt to reverse-engineer security controls or extract data that doesn't belong to you.
Misrepresent the Calculator's output as official HMRC guidance or financial advice.
Embed or redistribute the Calculator's output in a way that removes the disclaimers in §2.

7. API usage

The public API at /api/calculate/<mode>/ is provided as-is under the same terms as the rest of the service. Specifically:

Anonymous traffic is throttled (60 requests/minute per IP).
The API is not suitable for high-volume production traffic in its current state. A paid tier with authenticated access will be added later.
We may change the API surface, add new endpoints, or remove endpoints at any time. The latest documentation lives at /api-docs/.
Output should not be redisplayed without the disclaimers in §2.

8. Privacy

What we collect, why, and how long we keep it is in our Privacy Policy: /privacy/.

9. Changes to these terms

We may update these terms. The "Last updated" date at the top will reflect any change. Material changes (e.g. new use restrictions) will be flagged on the site for at least 30 days. By continuing to use the Calculator after a change, you accept the new terms.

10. Governing law

These terms are governed by the laws of England and Wales. Any disputes will be heard in the courts of England and Wales.

11. Contact

Use the contact form. For data / privacy questions, pick the "Data / privacy request (GDPR)" subject in the dropdown. Service is operated by Loglux Ltd (Company No. NI739810, registered in Northern Ireland).