Your bill can arrive later
The money may feel available when it lands, even though some of it may need to cover future tax.
Tax reserve calculator for self-employed users
Estimate how much tax you may want to set aside as a UK self-employed user, including rough planning for Self Assessment and possible payments on account.
This is a planning guide, not a final tax calculation. It uses the figures you enter and does not connect to HMRC.
Why a tax reserve matters
When you are self-employed, tax is often not taken automatically from each payment. A reserve helps you keep part of your income mentally separate before the deadline arrives.
A rough percentage is useful
Even an imperfect estimate can help you build a safer habit than waiting until the return is due.
Review it as figures change
Income, expenses and payments already made can change the amount you may want to keep aside.
Enter your details
Use rough figures if that is all you have. The result is designed to give you a practical starting point.
Choose the year you want this estimate to apply to.
Estimate mode
Use the mode that best matches the figures you have.
Before expenses, for the selected tax year.
Add this only if it applies to you.
Optional. Leave as zero if you only want a simple income-based estimate.
Optional. Use this to compare your current set-aside with the estimate.
How this estimate works
The calculator starts with the figures you enter, estimates a rough profit position, then turns that into a planning reserve. The goal is not exactness — it is to help you avoid spending money that may later be needed for tax.
- Income is based on your self-employment and property income entries.
- Expenses can reduce the rough profit used for the estimate.
- Already-set-aside money helps show what may still be left to reserve.
- The result should be reviewed as your real records become clearer.
Keeping clearer records can make your reserve estimate more useful. Read the records guide.
What your reserve may need to cover
A tax reserve is not just a single number. Depending on your situation, several parts can affect how much cash you want to keep available.
Income Tax
Your taxable profit may fall into different tax bands after allowances and other factors.
National Insurance
Self-employed users may need to think about Class 4 National Insurance when profits are above the relevant threshold.
Payments on account
Some Self Assessment users also need advance payments towards the next bill, which can make January feel larger.
Think in tax-year checkpoints
The exact dates depend on your Self Assessment position, but these checkpoints are useful when planning a reserve habit.
Set aside as income arrives
A small reserve habit is easier than trying to find the whole amount at once.
Main Self Assessment payment point
This can include your balancing payment and, for some users, a first payment on account.
Possible second payment on account
If payments on account apply, the second instalment is usually due later in the year.
How to read your result
Treat the result as a calm planning number. It should help you decide whether your current set-aside feels reasonable, not tell you your final tax bill.
- If your income is estimated, your reserve should be reviewed later.
- If your expenses are incomplete, your rough profit may be too high or too low.
- If your Self Assessment position is complex, use this as a prompt to check official guidance or ask an adviser.
Tax reserve calculator FAQs
Short answers before you use the calculator.
Is this my final tax bill?
No. This is a planning estimate based on the details you enter. Your final tax bill can depend on allowances, other income, reliefs, payments already made and your exact Self Assessment position.
Should I enter income before or after expenses?
Enter income before expenses in the income fields. Use the expenses field separately if you want the estimate to consider a rough net profit.
Why include money already set aside?
It helps compare your current savings with the rough reserve estimate, so you can see whether there may be more to set aside.
Does this include payments on account?
The result should be treated carefully. Payments on account can affect cash planning for some Self Assessment users, so check your HMRC account or official guidance if this applies to you.
Can I use monthly income?
Yes, if the existing calculator supports monthly mode. Use the mode that best matches the figures you currently have.
How often should I update the estimate?
Review it when income changes, expenses become clearer, or you have already set aside more money.
Keep your reserve connected to the rest of your year
SelfYear helps you connect records, deadlines, notices and practical planning prompts into one calmer self-employed year view.