The formula is simply
10000 x 1.05^5
or, in words, ten thousand times one point oh five to the power five
where 10000 is the sum invested
1.05 is 1 plus the interest rate (5% = 5 per 100 = 5/100 = 0.05)
5 is the number of years
1.05 to the power 5 is 1.05 multiplied by itself 5 times in total, in other words 1.05 x 1.05 x 1.05 x 1.05 x 1.05
In Excel the formula is
=10000*POWER(1.05,5)
On a scientific calculator you would press these keys:
10000 x 1.05 yx 5 =
where "yx" is a key with a big y and a little x next to and higher than the y
On a simple calculator you would have to do this:
10000 x 1.05 x 1.05 x 1.05 x 1.05 x 1.05 =
These all give the answer: £12762.82 (rounded to the nearest penny)
If tax is due then the net interest rate is 4%, so the formula becomes
10000 x 1.04^5
Giving: £12166.53