No Claim Discount (NCD) is a form of premium discount for not having made a claim during the preceding period of your insurance (provided that the period of insurance exceeds one year).
The applicable NCD will increase with each renewal if you continue to have claim-free years as shown in the scale below:
After 1 continuous claim-free year - 25%
After 2 continuous claim-free years - 30%
After 3 continuous claim-free years - 38.33%
After 4 continuous claim-free years - 45%
After 5 continuous claim-free years and beyond - 55%