How are the Tbills allotted and how are the yields of the Tbills allotted to me determined?
Tbills are issued via a uniformprice auction. This means that all successful applications, whether noncompetitive or competitive, will be allotted the Tbills at a uniform yield, which is the cutoff yield. The cutoff yield of the Tbills auction is the highest accepted yield of successful competitive applications submitted at the auction.
In a Tbills auction, allotment starts with the noncompetitive applications, followed by the competitive applications:
 Noncompetitive applications are allotted first, up to 40% of the total issuance amount. If the total amount of noncompetitive applications exceeds 40%, the Tbills will be allotted to noncompetitive applications on a prorated basis. However, to ensure that the final allotments are in denominations of S$1,000, adjustments will be made by the system on a randomised basis.
 The rest of the issuance amount will be awarded to competitive applications, starting from the lowest to the highest yields submitted.
Illustration
Here is a stylised example to illustrate the allotment process for Tbills, which assumes:
Total Issuance Size of Tbills  S$20,000 
Total Noncompetitive Applications Received  S$8,000 
Total Competitive ApplicationsReceived  S$18,000 
For this example, the allotment will be as follows:
 The noncompetitive applications will be allotted first. As the noncompetitive applications of S$8,000 is within 40% of the issuance size (i.e. S$8,000), the noncompetitive applications will be fully allotted. This means that everyone who submitted a noncompetitive application will be allotted the amount that they had bid for, capped at S$1 million per Tbills auction.
 The competitive applications will be allotted next based on the remaining auction amount of S$12,000. The applications will be allotted starting with the lowest yield, and move to the next lowest yield and so on until the remaining auction amount of S$12,000 is reached.
Competitive or Noncompetitive  Application amount  Allotment amount  Cumulative allotment amount  Remarks 
Noncompetitive applications (A)  S$1,000  S$1,000 (fully allotted)  S$1,000  
Noncompetitive applications (B)  S$3,000  S$3,000 (fully allotted)  S$4,000  
Noncompetitive applications (C)  S$4,000  S$4,000 (fully allotted)  S$8,000  
Total of Noncompetitive applications  S$8,000  S$8,000 (100% of noncompetitive applications allotted)  S$8,000  In this example, the noncompetitive applications were 100% allotted as the total amount of noncompetitive applications was within 40% of the total issuance amount. 
Competitive applications at 1%  S$3,000  S$3,000 (fully allotted)  S$11,000  All applications at this yield were fully allotted as it is below the cutoff yield. 
Competitive applications at 2%  S$4,000  S$4,000 (fully allotted)  S$15,000  All applications at this yield were fully allotted as it is below the cutoff yield. 
Competitive applications at 3%  S$4,000  S$4,000 (fully allotted)  S$19,000  All applications at this yield were fully allotted as it is below the cutoff yield. 
Competitive applications at 4%  S$5,000  S$1,000 (prorated allotment)  S$20,000 

Competitive applications at 5%  S$2,000      Applications at this yield were not allotted as the total issuance size has been met. 
Total of Competitive applications  S$18,000  S$12,000  S$20,000  4% becomes the cutoff yield for this auction. 
In summary  
Total of both Noncompetitive and Competitive applications  S$26,000 (Noncompetitive S$8,000, Competitive S$18,000)  S$20,000 (Noncompetitive S$8,000, Competitive S$12,000)  S$20,000  Cutoff yield = 4%. 
In this example, the cutoff yield is 4%. All allotted applications, noncompetitive and competitive, will receive the same cutoff yield of 4%.
This information is sourced from MAS