Tax Bill Savings Calculator
If you're self-employed, receive dividend income, or have capital gains, HMRC will expect you to pay tax that wasn't deducted at source. Self Assessment deadlines fall in January and July.
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A common mistake is waiting until the tax bill arrives to start saving. By then, you may not have the cash available, especially if your first Self Assessment includes payments on account – advance payments towards next year's bill.
Setting aside money monthly keeps your tax obligations manageable. As a rule of thumb, save 25-30% of untaxed income for basic rate taxpayers, or 40-45% for higher rate. Enter your expected tax bill below to calculate how much to save each month.
Your Tax Details
Income not yet taxed through PAYE
Effective rate for income: 40% + NI
Savings Plan
Self-assessment: 31 Jan / 31 Jul • CGT: 60 days after sale
Savings Target
Estimated Tax Bill
£0
Based on 40% + NI rate
Still to Save
£0
Monthly Required
£0
You're Covered
Your current savings cover the estimated tax bill.
Key Dates
- • Self-assessment: 31 January (balancing payment + first POA)
- • Second POA: 31 July
- • Capital gains: 60 days after property sale
- • Late payment: Interest + 5% penalty after 30 days
Understanding Emergency Tax Bills
Tax bills often catch people off guard—especially those with income outside PAYE. Self-employment, dividends, rental income, and capital gains all create tax liabilities that aren't collected at source, leading to potentially large bills months after you received the money.
Why Tax Bills Arrive Unexpectedly
Unlike PAYE workers who have tax deducted automatically, several types of income are taxed later:
- Self-employment: Profits are taxed in arrears, plus you make payments on account for next year
- Rental income: Collected through self-assessment, often 10-22 months after receiving rent
- Dividends: Taxed via self-assessment if over the £500 allowance
- Capital gains: Property CGT due in 60 days; other gains via self-assessment
- High earners: Child benefit clawback, personal allowance reduction, pension limits
The Timing Trap
The gap between earning money and paying tax creates a dangerous timing trap. You might receive £20,000 in January, spend it by August, then face an £8,000 tax bill the following January. This is especially problematic for:
- New freelancers who haven't experienced a full tax cycle
- People who receive irregular large payments (bonuses, project fees)
- Property sellers facing CGT within 60 days
- Anyone moving from PAYE to self-employment
Ring-Fencing Your Tax Money
The solution is simple but requires discipline: treat tax money as not yours from the moment you earn it.
- Separate account: Open a dedicated savings account just for tax
- Automatic transfers: Move 25-40% of each payment immediately
- Earn interest: An instant-access savings account earns while you wait
- Never touch it: This money is already spent—it belongs to HMRC
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