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Calculator: Weight-for-age percentiles and Z-scores, 0 to 24 months (WHO)

Calculator: Weight-for-age percentiles and Z-scores, 0 to 24 months (WHO)

 
Input
 
Sex Female

 Male
Age  
Weight  

 
Results
 
Important: Inputs must be complete to perform calculation.

 
 
Z-score    
Percentile    
 
Decimal precision  
 

 
 

 
Notes
  • This calculator is based on the World Health Organization (WHO) growth standard.
  • Weight percentiles are best interpreted with reference to height (refer to the calculator for infant weight for length percentiles).
  • At the extremes (>97th percentile or <3rd percentile), small differences in percentiles represent clinically important differences. At these extremes, the Z-score is a more precise reflection of how far the measurement deviates from the mean and is a useful tool for tracking changes.
  • For all LMS tables, the row in the table corresponding to the patient-specific value is found in the first column of the table; values to be used for L (the Box-Cox power), M (the median), and S (the generalized coefficient of variation) in the equation for Z-score are retrieved.
  • The accuracy of the calculation can be assessed by viewing the graph of weight-for-age percentiles for this sex and age group in UpToDate.
  • Z-scores may be used to perform a table lookup for the corresponding percentile in the Normal table percentiles for Z-score table (below). Numbers along the left side (Y-axis) of the table represent the first number and first decimal place of the Z-score, while the numbers along the top (X-axis) of the table represent the second decimal position of the Z-score.

 
Equations used
 
Z_Score = ((Weight/M)L - 1) / (L * S)
Percentile = ZtoPercentile(Z-score)

 

 
References
  1. World Health Organization. The WHO Child Growth Standards. https://www.who.int/childgrowth/standards/en/ (Accessed on June 26, 2023).

 
Appendix

 
LMS table: Weight-for-age percentiles, females 0 to 24 months, WHO growth standard
 
Age [months] Power [L] Median [M] Variation [S]
0 0.3809 3.2322 0.1417
1 0.1714 4.1873 0.1372
2 0.0962 5.1282 0.1300
3 0.0402 5.8458 0.1262
4 -0.0050 6.4237 0.1240
5 -0.0430 6.8985 0.1227
6 -0.0756 7.2970 0.1220
7 -0.1039 7.6422 0.1218
8 -0.1288 7.9487 0.1218
9 -0.1507 8.2254 0.1220
10 -0.1700 8.4800 0.1222
11 -0.1872 8.7192 0.1225
12 -0.2024 8.9481 0.1227
13 -0.2158 9.1699 0.1228
14 -0.2278 9.3870 0.1229
15 -0.2384 9.6008 0.1230
16 -0.2478 9.8124 0.1230
17 -0.2562 10.0226 0.1231
18 -0.2637 10.2315 0.1231
19 -0.2703 10.4393 0.1231
20 -0.2762 10.6464 0.1232
21 -0.2815 10.8534 0.1234
22 -0.2862 11.0608 0.1235
23 -0.2903 11.2688 0.1237
24 -0.2941 11.4775 0.1239

 
LMS table: Weight-for-age percentiles, males 0 to 24 months, WHO growth standard
 
Age [months] Power [L] Median [M] Variation [S]
0 0.3487 3.3464 0.1460
1 0.2297 4.4709 0.1340
2 0.1970 5.5675 0.1239
3 0.1738 6.3762 0.1173
4 0.1553 7.0023 0.1132
5 0.1395 7.5105 0.1108
6 0.1257 7.9340 0.1096
7 0.1134 8.2970 0.1090
8 0.1021 8.6151 0.1088
9 0.0917 8.9014 0.1088
10 0.0820 9.1649 0.1089
11 0.0730 9.4122 0.1091
12 0.0644 9.6479 0.1092
13 0.0563 9.8749 0.1095
14 0.0487 10.0953 0.1098
15 0.0413 10.3108 0.1101
16 0.0343 10.5228 0.1104
17 0.0275 10.7319 0.1108
18 0.0211 10.9385 0.1112
19 0.0148 11.1430 0.1116
20 0.0087 11.3462 0.1121
21 0.0029 11.5486 0.1126
22 -0.0028 11.7504 0.1131
23 -0.0083 11.9514 0.1137
24 -0.0137 12.1515 0.1143

 
LMS table: Normal table percentiles for Z-score
 
Z 1 3 5 7 9
-3.0 0.13% 0.12% 0.11% 0.11% 0.10%
-2.9 0.18% 0.17% 0.16% 0.15% 0.14%
-2.8 0.25% 0.23% 0.22% 0.21% 0.19%
-2.7 0.34% 0.32% 0.30% 0.28% 0.26%
-2.6 0.45% 0.43% 0.40% 0.38% 0.36%
-2.5 0.60% 0.57% 0.54% 0.51% 0.48%
-2.4 0.80% 0.75% 0.71% 0.68% 0.64%
-2.3 1.04% 0.99% 0.94% 0.89% 0.84%
-2.2 1.36% 1.29% 1.22% 1.16% 1.10%
-2.1 1.74% 1.66% 1.58% 1.50% 1.43%
-2.0 2.22% 2.12% 2.02% 1.92% 1.83%
-1.9 2.81% 2.68% 2.56% 2.44% 2.33%
-1.8 3.52% 3.36% 3.22% 3.07% 2.94%
-1.7 4.36% 4.18% 4.01% 3.84% 3.67%
-1.6 5.37% 5.16% 4.95% 4.75% 4.55%
-1.5 6.55% 6.30% 6.06% 5.82% 5.59%
-1.4 7.93% 7.64% 7.35% 7.08% 6.81%
-1.3 9.51% 9.18% 8.85% 8.53% 8.23%
-1.2 11.31% 10.94% 10.57% 10.20% 9.85%
-1.1 13.35% 12.92% 12.51% 12.10% 11.70%
-1.0 15.63% 15.15% 14.69% 14.23% 13.79%
-0.9 18.14% 17.62% 17.11% 16.60% 16.11%
-0.8 20.90% 20.33% 19.77% 19.22% 18.67%
-0.7 23.89% 23.27% 22.66% 22.07% 21.48%
-0.6 27.09% 26.44% 25.79% 25.14% 24.51%
-0.5 30.50% 29.81% 29.12% 28.43% 27.76%
-0.4 34.09% 33.36% 32.64% 31.92% 31.21%
-0.3 37.83% 37.07% 36.32% 35.57% 34.83%
-0.2 41.68% 40.91% 40.13% 39.36% 38.59%
-0.1 45.62% 44.83% 44.04% 43.25% 42.47%
-0.0 49.60% 48.80% 48.01% 47.21% 46.41%
0.0 50.40% 51.20% 51.99% 52.79% 53.59%
0.1 54.38% 55.17% 55.96% 56.75% 57.54%
0.2 58.32% 59.10% 59.87% 60.64% 61.41%
0.3 62.17% 62.93% 63.68% 64.43% 65.17%
0.4 65.91% 66.64% 67.36% 68.08% 68.79%
0.5 69.50% 70.19% 70.88% 71.57% 72.24%
0.6 72.91% 73.57% 74.22% 74.86% 75.49%
0.7 76.12% 76.73% 77.34% 77.94% 78.52%
0.8 79.10% 79.67% 80.23% 80.79% 81.33%
0.9 81.86% 82.38% 82.89% 83.40% 83.89%
1.0 84.38% 84.85% 85.31% 85.77% 86.21%
1.1 86.65% 87.08% 87.49% 87.90% 88.30%
1.2 88.69% 89.07% 89.44% 89.80% 90.15%
1.3 90.49% 90.82% 91.15% 91.47% 91.77%
1.4 92.07% 92.36% 92.65% 92.92% 93.19%
1.5 93.45% 93.70% 93.94% 94.18% 94.41%
1.6 94.63% 94.85% 95.05% 95.25% 95.45%
1.7 95.64% 95.82% 95.99% 96.16% 96.33%
1.8 96.49% 96.64% 96.78% 96.93% 97.06%
1.9 97.19% 97.32% 97.44% 97.56% 97.67%
2.0 97.78% 97.88% 97.98% 98.08% 98.17%
2.1 98.26% 98.34% 98.42% 98.50% 98.57%
2.2 98.65% 98.71% 98.78% 98.84% 98.90%
2.3 98.96% 99.01% 99.06% 99.11% 99.16%
2.4 99.20% 99.25% 99.29% 99.32% 99.36%
2.5 99.40% 99.43% 99.46% 99.49% 99.52%
2.6 99.55% 99.57% 99.60% 99.62% 99.64%
2.7 99.66% 99.68% 99.70% 99.72% 99.74%
2.8 99.75% 99.77% 99.78% 99.80% 99.81%
2.9 99.82% 99.83% 99.84% 99.85% 99.86%
3.0 99.87% 99.88% 99.89% 99.89% 99.90%

 
Only digits 0 to 9 and a single decimal point (".") are acceptable as numeric inputs. Attempted input of other characters into a numeric field may lead to an incorrect result.

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All information contained in and produced by the EBMcalc system is provided for educational purposes only. This information should not be used for the diagnosis or treatment of any health problem or disease. THIS INFORMATION IS NOT INTENDED TO REPLACE CLINICAL JUDGMENT OR GUIDE INDIVIDUAL PATIENT CARE IN ANY MANNER.

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Topic 15632 Version 16.0

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