UK Self-Assessment Tax Calculator (Income Tax & Class 2/4 National Insurance)
Estimate UK Self-Assessment income tax and Class 2/Class 4 National Insurance contributions for the 2023/24 tax year. Provides methodology, sources (HMRC), and author/last-updated details.
- Page updated:
- Jun 1, 2024
- Tool version:
- v1.1.0
Overview
Estimate your UK Self-Assessment Income Tax and Class 2/4 National Insurance contributions for the 2023/24 tax year. This calculator uses HMRC thresholds and rates to provide a quick estimate — it is for guidance only and does not replace HMRC calculations or professional tax advice.
Results
Total Estimated Liability (GBP)
$3,486.00
Taxable after personal allowance
$17,430.00
Income taxed at basic rate
$17,430.00
Income taxed at higher rate
$0.00
Income taxed at additional rate
$0.00
Income Tax (GBP)
$3,486.00
Class 2 National Insurance (GBP)
$0.00
Class 4 NIC portion (lower rate)
$0.00
Class 4 NIC portion (upper rate)
$0.00
Class 4 National Insurance (GBP)
$0.00
How to read the result
- What it means
- The displayed value is an estimate based on your inputs. It represents the calculated scenario under current assumptions, not a guaranteed amount.
- Next step
- Use the result as a starting point. Adjust parameters to compare scenarios and validate with a professional when needed.
- Calculation limits
- The model uses simplified formulas and cannot account for all variables in your specific case (local regulations, personal conditions, temporal changes).
Methodology
Personal allowance and income tax bands follow HMRC 2023/24 rules: personal allowance £12,570; basic rate 20% up to £50,270; higher rate 40% up to £125,140; additional rate 45% above £125,140.
Class 2 NIC is estimated as a flat weekly rate applied when self-employed profits exceed the Small Profits Threshold. Class 4 NIC is calculated as 9% on profits between the Lower Profits Threshold and Upper Profits Threshold, and 2% on profits above the Upper Profits Threshold.
All inputs must reflect taxable figures for the tax year after allowable deductions. The calculator rounds figures for display; final liabilities may differ due to other allowances, reliefs, student loan repayments, pension contributions, or adjustments.
Glossary+−
- Personal Allowance
The amount of income you can receive each year without paying income tax.
- Class 2 National Insurance
A flat-rate weekly National Insurance contribution payable by self-employed people who earn above the Small Profits Threshold.
- Class 4 National Insurance
A profits-based National Insurance contribution payable by self-employed people, charged as a percentage on profits within specified thresholds.
Key takeaways
This calculator provides an HMRC-aligned estimate of Income Tax and Class 2/4 National Insurance for the 2023/24 tax year. Use the inputs to model different scenarios; consult HMRC or a qualified adviser for definitive calculations.
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Worked examples
Example: Employed individual (no self-employment)
Taxable income £30,000, not self-employed. Calculator estimates income tax on taxable income after personal allowance; no Class 2 or Class 4 NIC applied.
Interpretation
Provides an estimate of income tax only. For employed people, PAYE and National Insurance contributions paid via payroll are not modelled here.
Example: Self-employed sole trader
Taxable income £35,000 with £30,000 taxable profits from self-employment. Calculator estimates Income Tax plus Class 2 and Class 4 NIC using HMRC thresholds.
Interpretation
Estimate includes income tax after personal allowance and both Class 2 (if above threshold) and Class 4 contributions on profits.
Frequently asked questions
Does this calculator include student loan or pension adjustments?
No. This tool estimates Income Tax and Class 2/4 NIC only. It does not include student loan repayments, pension tax relief, or other deductions. For full calculations include those items or use HMRC services / a tax adviser.
Are the rates current?
Rates and thresholds reflect the 2023/24 tax year and are cited to HMRC pages. See citations for official sources. We update this page periodically; check the last-updated date in the metadata.
Sources & references
- HM Revenue & Customs - Income Tax rates and Personal Allowances: https://www.gov.uk/income-tax-rates
- HM Revenue & Customs - National Insurance for the self-employed: https://www.gov.uk/self-employed-national-insurance-rates
- HM Revenue & Customs - Guide to Self Assessment: https://www.gov.uk/self-assessment-tax-returns
Quality & oversight
- Author
- Ugo Candido, MBA
- Maintained by
- Ugo Candido, MBA
- Page updated
- Jun 1, 2024
- Tool version
- v1.1.0