Calculating Percentage of Delay

Percentage Delay Conversion Chart*

Chronological Age

Age Equivalent in Months with % Delay

Chronological Age

Age Equivalent in Months with % Delay

Age in Years

(Y= Years; M= Months)

Age in Months

25% Delay

33% Delay

> 50% Delay

Age in Years

(Y= Years; M= Months)

Age in Months

25% Delay

33% Delay

> 50% Delay

0 Y 4 M

4

3

2.7

<2

1 Y 8 M

20

15

13.4

<10

0 Y 5 M

5

3.8

3.4

<2.5

1 Y 9 M

21

15.8

14.1

<10.5

0 Y 6 M

6

4.5

4

<3

1 Y 10 M

22

16.5

14.7

<11

0 Y 7 M

7

5.3

4.7

<3.5

1 Y 11 M

23

17.3

15.4

<11.5

0 Y 8 M

8

6

5.4

<4

2 Y 0 M

24

18

16.1

<12

0 Y 9 M

9

6.8

6

<4.5

2 Y 1 M

25

18.8

16.8

<12.5

0 Y 10 M

10

7.5

6.7

<5

2 Y 2 M

26

19.5

17.4

<13

0 Y 11 M

11

8.3

7.4

<5.5

2 Y 3 M

27

20.3

18.1

<13.5

1 Y 0 M

12

9

8

<6

2 Y 4 M

28

21

18.8

<14

1 Y 1 M

13

9.8

8.7

<6.5

2 Y 5 M

29

21.8

19.4

<14.5

1 Y 2 M

14

10.5

9.4

<7

2 Y 6 M

30

22.5

20.1

<15

1 Y 3 M

15

11.3

10.1

<7.5

2 Y 7 M

31

23.3

20.8

<15.5

1 Y 4 M

16

12

10.7

<8

2 Y 8 M

32

24

21.4

<16

1 Y 5 M

17

12.8

11.4

<8.5

2 Y 9 M

33

24.8

22.1

<16.5

1 Y 6 M

18

13.5

12.1

<9

2 Y 10 M

34

25.5

22.8

<17

1 Y 7 M

19

14.3

12.7

<9.5

2 Y 11 M

35

26.3

23.5

<17.5

*Adapted from Step by Step Infant Development Center Percentage Delay Conversion Chart.