Number Bonds Calculator

Work out number bonds instantly with clear inputs, formula shown and shareable results.

About Number Bonds Calculator

The missing part is the total minus the known part; whole-number ordered pairs number total + 1, and unordered pairs floor(total / 2) + 1. Instant recall of bonds to 10 and 20 is what allows children to add by bridging rather than counting on their fingers.

Formulas

Missing part

missing = total - known part

How many bonds

ordered pairs = total + 1; unordered pairs = floor(total / 2) + 1

Worked example

With the default values below, Number Bonds Calculator returns Missing part of 6. Change any input above and every figure here is recalculated in your browser.

Inputs used

Bond totalminimum 1: 10
One partminimum 0: 4

Results

Missing part: 6
The bond written out: 4 + 6 = 10
Ordered pairs that make the total: 11
Unordered pairs: 6

Step by step

1Values used
2Missing part
3How many bonds
4Missing part= 6
5The bond written out= 4 + 6 = 10
6Ordered pairs that make the total= 11
7Unordered pairs= 6

Assumptions and limits

The result is derived only from the 2 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to whole numbers, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How is the Number Bonds figure worked out?

missing = total - known part. The missing part is the total minus the known part; whole-number ordered pairs number total + 1, and unordered pairs floor(total / 2) + 1.

Why does this matter?

Instant recall of bonds to 10 and 20 is what allows children to add by bridging rather than counting on their fingers.

What do I need to enter?

Enter bond total, one part. The defaults shown are a realistic worked example — swap in your own figures to get a result you can use.