Reasonable is not a legal test in a settlement agreement. The Act does not require the sum to be fair, only that the conditions in section 203 are met before your statutory claims are waived. So the honest way to answer this question is not to quote a figure, which nobody publishes, but to give you the two things a reasonable offer can be measured against: the statutory floor and the tax treatment.
The floor, which is not negotiable and is easy to check
In a redundancy the offer should not be below what is payable anyway. That is the statutory redundancy payment under section 162 of the Employment Rights Act 1996, computed from the age bands with service capped at 20 years and a week's pay capped at 751 pounds for a redundancy on or after 6 April 2026, to a maximum of 22,530 pounds; plus the statutory or contractual notice under section 86; plus accrued untaken holiday. An offer at or near that total is buying your waiver for nothing, because all of it was owed.
The tax line, which decides what reasonable means in cash
Two offers with the same headline are not equally reasonable if they apportion differently. The sum attributable to notice is taxed as earnings. Other termination money counts as employment income only to the extent it exceeds the 30,000 pound threshold in section 403 of the Income Tax (Earnings and Pensions) Act 2003, and GOV.UK states plainly that statutory redundancy pay under 30,000 pounds is not taxable. Comparing offers on the headline rather than after that apportionment is the commonest way people accept the worse one.
What is being given up on the other side
The agreement is a purchase, so what it costs should reflect what it buys. Acas lists what an agreement can contain: a financial payment, an employment reference, an agreement not to make a tribunal claim, and a confidentiality clause. A waiver of a strong claim is worth more than a waiver of a weak one, and confidentiality and a covenant have value to the employer that is separate from the dismissal itself. Whether your particular claim is strong is exactly the assessment the independent adviser is there to make, and it is not something this site can do from published rules.
Why no page can honestly give you a number
Settlement agreements are private and usually confidential, so there is no published dataset of what people receive, no regulator return and no register. Tribunal awards are published but measure something else: what a claim was worth after a hearing, not what an employer paid to avoid one. This site records that no such figure is published rather than inventing a multiple of salary, because a benchmark nobody measured would be the least reliable input into the one decision that matters here.
Other questions people ask
Is there a rule of thumb, like a month per year of service?
Not one that is published or measured. Rules of thumb circulate, but there is no dataset behind them because settlement agreements are private. The floor you can verify is the statutory redundancy payment plus notice plus accrued holiday.
How do I compare two offers?
Apportion each into arrears, notice and ex gratia, then apply the tax treatment: notice as earnings, the rest against the 30,000 pound threshold in section 403. The larger headline is not always the larger payment.
Can this site tell me whether my offer is fair?
No, and it does not try. Fairness depends on the strength of a claim on your own facts, which is an assessment for the relevant independent adviser section 203 requires you to see anyway.