Because retrenchment benefits in Singapore are contractual rather than statutory, the order of checking is different from most countries.
One: your employment contract
The terms outline the details of the agreement and are binding on both parties. This is your first recourse.
Look for a retrenchment or severance clause specifically.
Two: company policy
Followed by internal policies or other regulations. Some companies have a written retrenchment policy even where the contract is silent.
Three: any collective agreement
If a union covers your workplace, the collective agreement may provide for retrenchment benefits — and unionised firms typically pay a full month per year of service.
Four: the market norm as a reference
Two weeks to one month of salary per year of service, per MOM's Tripartite Advisory.
It is a recommendation, not a mandate, but it is the benchmark against which an offer can be assessed.