How to Calculate Tax Deductions From Your Salary

The gap between the salary you agreed to and the amount that lands in your account is often larger than people expect. A payslip lists several deductions, applied in a specific order, and each is calculated on a different base.

That order matters more than it looks. Some deductions come out before income tax is calculated, which reduces the tax you owe. Others come out afterwards and do not. Knowing which is which is the difference between guessing at your net pay and being able to work it out.

This guide walks through each deduction type, explains the sequence, and works a complete example from gross to net.

The Two Kinds of Deduction

Everything taken from your salary falls into one of two categories, and the distinction determines how much tax you pay.

Pre-tax deductions are subtracted from gross pay before income tax is calculated. They reduce your taxable income, so they reduce your tax bill as a side effect. A contribution of 100 costs you less than 100 in take-home pay.

Post-tax deductions come out after tax has been calculated. They reduce your take-home pay by exactly their face value and provide no tax benefit.

Typically Pre-Tax	Typically Post-Tax
Workplace pension contributions	Union dues
Certain health insurance schemes	Loan or salary advance repayments
Salary sacrifice arrangements	Court-ordered deductions
Some commuter and childcare benefits	Charitable giving (in some systems)

The Order Deductions Are Applied

Payroll follows a sequence. Changing the order changes the answer, which is why working through it properly matters.

1. Start with gross pay – your full salary for the period, including any bonus or overtime.
2. Subtract pre-tax deductions – pension contributions and similar schemes. The result is your taxable income.
3. Calculate income tax on that taxable income, using the applicable brackets.
4. Calculate payroll or social security contributions – note these are usually based on gross pay, not the reduced taxable figure.
5. Subtract post-tax deductions – anything remaining.
6. What is left is your net pay.

Step four is the one that surprises people. Social security and payroll contributions are commonly assessed on gross earnings, so a pension contribution that saves you income tax may not reduce those contributions at all.

Worked Example: A Salary of 60,000

Take an annual gross salary of 60,000, with a 5% pension contribution, a payroll contribution rate of 7.65% on gross, and health cover at 1,800 a year. Using the illustrative tax brackets from our tax bracket guide (0% to 10,000, 10% to 40,000, 22% to 85,000).

Step 1 – Pre-tax deduction

Pension at 5% of 60,000 = 3,000

Taxable income = 60,000 – 3,000 = 57,000

Step 2 – Income tax on 57,000

• First 10,000 at 0% = 0
• Next 30,000 at 10% = 3,000
• Next 17,000 at 22% = 3,740
• Total income tax = 6,740

Step 3 – Payroll contribution on gross

7.65% of 60,000 = 4,590

Note this is calculated on the full 60,000, not on 57,000.

Step 4 – Post-tax deduction

Health cover = 1,800

Step 5 – Net pay

60,000 – 3,000 – 6,740 – 4,590 – 1,800 = 43,870

Monthly net = 43,870 / 12 = 3,655.83

The Full Picture

Laid out as a payslip would show it:

Total deductions are 16,130, an effective deduction rate of 26.88%. Note that income tax is only 11.23% of gross – less than half of the total taken. People tend to attribute the whole gap to income tax, when payroll contributions and benefits account for the majority of it here.

Item	Annual	Monthly	% of Gross
Gross salary	60,000	5,000.00	100%
Pension (pre-tax)	-3,000	-250.00	5.00%
Income tax	-6,740	-561.67	11.23%
Payroll contribution	-4,590	-382.50	7.65%
Health cover (post-tax)	-1,800	-150.00	3.00%
Net pay	43,870	3,655.83	73.12%

Why Pre-Tax Contributions Cost Less Than They Look

The 3,000 pension contribution in the example did not reduce take-home pay by 3,000. Because it lowered taxable income from 60,000 to 57,000, it also removed 22% tax on that 3,000 – a saving of 660.

So the real cost to take-home pay was 3,000 – 660 = 2,340, while 3,000 went into the pension.

This effect is why pre-tax contributions are usually the most efficient way to save, and why they are worth more to higher earners. If your employer also matches contributions, the return is higher still.

Marginal Rate	Contribution	Tax Saved	Real Cost to You
10%	3,000	300	2,700
22%	3,000	660	2,340
24%	3,000	720	2,280
32%	3,000	960	2,040

Checking Your Payslip for Errors

Payroll mistakes are more common than most people assume, and they can persist for months unnoticed. Check these:

• Your tax code or equivalent identifier. An incorrect code is the most frequent cause of over- or under-payment.
• Gross pay. Confirm overtime, bonuses, and any rate change are included correctly.
• Pension percentage. Verify it matches what you elected, and that any employer match is showing.
• Year-to-date totals. These should accumulate sensibly; a sudden jump or reset warrants a question.
• Any new deduction. Anything you did not authorize should be queried immediately.

If your own calculation and the payslip disagree by more than a rounding difference, ask payroll for a breakdown. Overpaid tax is usually recoverable, but the process is far simpler if you catch it in the same tax year.

Conclusion

Calculating net pay is a sequence, not a single subtraction. Take gross pay, remove pre-tax deductions to find taxable income, apply the tax brackets, add payroll contributions calculated on gross, then remove anything post-tax. In the example, 60,000 became 43,870 – and income tax accounted for less than half of the difference.

The most useful practical insight is that pre-tax contributions cost less than their face value. A 3,000 pension contribution at a 22% marginal rate reduces take-home pay by only 2,340. If you are deciding whether to increase yours, that is the number to weigh – not the headline amount.

Frequently Asked Questions

How do I calculate net pay from gross salary?

Subtract pre-tax deductions such as pension contributions from gross pay to get taxable income. Apply the income tax brackets to that figure, then calculate payroll or social security contributions on gross pay, and finally subtract any post-tax deductions. What remains is your net pay.

What is the difference between pre-tax and post-tax deductions?

Pre-tax deductions come out before income tax is calculated, so they reduce your taxable income and therefore your tax bill. Post-tax deductions come out afterwards and reduce take-home pay by their exact amount with no tax benefit.

Do pension contributions reduce my tax?

In most systems yes, if they are made pre-tax. A 3,000 contribution for someone at a 22% marginal rate saves 660 in income tax, so the actual reduction in take-home pay is 2,340. Note that payroll or social security contributions are often still calculated on gross pay.

Why is my take-home pay lower than I expected?

Income tax is usually only part of the total. In the worked example, income tax was 11.23% of gross while total deductions were 26.88%, with payroll contributions and benefit premiums making up the difference. Check your payslip for every line, not just the tax figure.

What should I do if my payslip looks wrong?

Compare it against your own gross-to-net calculation and check your tax code, pension percentage, and year-to-date totals first. If there is a real discrepancy, contact payroll promptly with your working. Errors caught within the same tax year are much simpler to correct.