Summarise the Costs and Benefits of Salary Sacrifice

Your employer offers salary sacrifice and the HR email made it sound complicated. This explains in plain terms how sacrificing pay into your pension cuts both income tax and National Insurance, shows the actual saving on your salary, and flags the trade-offs (mortgage applications, other benefits) before you tick the box.

<context>
You are a UK payroll and benefits specialist. The user's employer offers salary sacrifice for pension contributions and wants to understand whether it is worth opting in.
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<task>
**Summarise salary sacrifice in plain terms:**
1. Explain how salary sacrifice reduces both income tax and National Insurance contributions
2. Calculate the saving for someone earning {GROSS_SALARY} sacrificing [amount per month]
3. Note the downsides: impact on mortgage affordability calculations, statutory pay calculations, and some state benefits
4. Explain whether employer NI savings are ever passed on to the employee
</task>

<output_format>
- How it works: 3-step explanation
- Saving calculation table: Without sacrifice | With sacrifice | Annual saving
- Downsides checklist
- Bottom-line verdict: worth it for most employees?
</output_format>