Natural hail can cause significant damage on seed yield and yield contributing traits of canola (Brassica napus L.). Hail damage can be assessed by (i) type of damage such as stand reduction, stem cut-off, and leaf defoliation, (ii) level of damage, and (iii) plant growth stage. In this research, a simulated hail study was performed by applying nonuniform stand reduction treatments on canola grown in North Dakota, USA, over 5 site-years, in 2017 and 2018. The experiment was a randomized complete block design 4 × 5 factorial arrangement with four growth stages, rosette, bolting, 50%, and 90% flowering, when five stand reduction treatments were applied at 0 (control), 25%, 50%, 75%, and 90%. Growth stage and stand reduction were significant for seed yield where yield decreased as stage of treatment progressed and level of stand reduction increased. Regression equations were developed to estimate the seed yield reduction at each growth stage as stand reduction increased. Stand reduction also affected other traits where plant height was reduced as stand reduction increased, whereas 1000-seed weight, primary branches plant^-1, secondary branches plant^-1, pods plant^-1, seed yield plant^-1, plant biomass plant^-1, and harvest index plant^-1 increased as stand reduction increased. As growth stage progressed the number of primary branches plant^-1, secondary branches plant^-1, pods plant^-1, and harvest index plant^-1 decreased, whereas 1000-seed weight increased. The findings of differential yield losses by stand reduction will help producers and crop adjusters to assess the severity of hail damage in canola.