I count on my fingers using this method:

1. No fingers = 0, assume all values are cumulative unless stated otherwise.

2. Start with index finger on Right hand:

• 1 = Index
• 2 = Middle
• 3 = Ring
• 4 = Pinky
• 5 = Thumb

3. After five, clear hand and start from Thumb and go until 9 (Ring)

• 6 = Thumb
• 7 = Index … etc

4. Double digits are counted on Left hand*, following same process as 1-3.

• For example: 13 would be:
  • Left Hand: Index
  • Right Hand: Index, Middle, Ring
• For something like 47 would be:
  • Left Hand: Index, Middle, Ring, Pinky
  • Right Hand: Thumb, Index

Using this method, the highest you can count to is 109:

• Left Hand: Thumb, Index, Middle, Ring, Pinky
• Right Hand: Thumb, Index, Middle, Ring

You could also probably differentiate 5 and 10 by half-raising your thumb for 5, and full raise for 6-10.