Rating Calculation Breakdown
HereInAfter - GREYVILLE CONVENTION CENTRE C STAKES (For All Horses with a nett rating of 83 & below) (31 Jan 2025)
Merit Rating Before
Rating Change
Merit Rating After
Calculation Steps
Step 1: Identify Line Horse
The "Line Horse" is the reference horse used to measure the race. It's the equine version of golf's "par" - a consistent performer who ran to their expected level.
- First: Check if any horse is explicitly marked with 'L' (Line Horse) in the race data
- If not marked: Look at placed horses (1st, 2nd, or 3rd) who have a rating
- Select: Choose the highest-rated placed horse as the reference
Why? A placed horse with a high rating is likely to have run to their expected level, making them a reliable benchmark for measuring other horses' performances.
| Selected Line Horse: | Trippi T |
|---|---|
| Pre-Race Rating: | 77 |
| Finished: | 4 |
| Weight Performance: | 55.5 kg |
Step 2: Calculate Weight-For-Age (WFA) Allowance
Younger horses receive a weight allowance based on age, distance, and time of year. This compensates for their lack of physical maturity.
| Horse Age: | 4 years |
|---|---|
| Race Distance: | 1000m |
| Month: | Jan |
| WFA Allowance: | 6.0 kg |
Step 3: Calculate Drag Adjustment
Weight equivalent of the beaten margin. Based on the official NHRA drag effect table (Page 13 of Handicapping Guidelines).
| Beaten Margin: | 0 lengths |
|---|---|
| Distance: | 1000m |
| Drag Adjustment: | 1.0 kg (1 length ≈ 1.0kg at this distance) |
Step 4: Calculate Actual Weight Performance
The weight value of the horse's performance, accounting for weight carried, beaten margin, and WFA allowance.
Weight Performance = Weight Carried - Drag Adjustment - WFA Allowance
| Weight Carried: | 52.0 kg |
|---|---|
| Minus Drag Adjustment: | 1.0 kg |
| Minus WFA Allowance: | 6.0 kg |
| Actual Weight Performance: | 45.0 kg |
Step 5: Compare to Line Horse
Compare this horse's performance to the line horse to determine the race rating.
This Horse's Rating = Line Horse Rating - (Weight Diff × 2)
| HereInAfter | vs | Trippi T (Line) | |
|---|---|---|---|
| Weight Performance | 45.0 kg | 55.5 kg | |
| Pre-Race Rating | ? | 77 | |
| Weight Difference | 55.5 - 45.0 = 10.5 kg × 2 = 21 rating points | ||
| Calculated Race Rating | 77 - 21 = 56 | ||
Step 6: Apply Special Rules & Final Adjustment
The handicapper applies judgement based on the horse's overall profile, race circumstances, and special rules (maiden caps, layoff allowance, etc.).
| Pre-Race Rating: | 0 |
|---|---|
| Calculated Race Rating: | 56 |
| Official New Rating: | 72 |
| Final Adjustment: | 0 |
Formula Reference
Key Formulas:
- Weight Performance: Weight - Drag - WFA
- Drag Effect: Varies by distance (see benchmarks)
- Rating Points: 1 kg = 2 rating points
- WFA Scale: Based on Admiral Rous's 1855 table
Sources:
- NHA Handicapping Guidelines (Page 13-20)
- Official Weight-For-Age Scale
- Drag Effect of Weight Tables
- Special Rules (Maiden Caps, Layoff Allowance)