Stanley income tax calculator website calculations are wrong

Problem reported by Peter Whitfield 9 years ago


I have carried out some basic checks on your online calculator (Stanley) and have identified a number of issues with your calculations.


The Tax Free Allowance of £9205.00 is incorrectly showing £767.08 per month and £177.02 per week, these should be £767.42 and £177.11 respectively.

The reason for the difference is in the way you are calculating Freepay. At its most basic to correctly calculate you should take the tax code, add 9 to the end and divide by 12 or 52 before rounding up the answer to the nearest penny. (To exactly calculate however you should really take into account the fact the code is a value over 500 and therefore use the specific freepay calc for these types.

Your software appears to add 5 instead of 9 and then rounds normally therefore giving the differences in the amounts.

eg Code 920L should be 9209/12 = 767.4166 which should round to 767.42.

There is also a difference in your National Insurance calculation, for a value of £2000.00 pay, you get NI of:

Employee: £162.52

Employer: £186.90

However these should be £162.48 and £187.54 I am unable to easily see how you have reached these figures as the results obtained dont require rounding.

E'ee (£1354 x 12%) = 162.4800 and therefore no rounding required.

E'er (£5 x 13.8%) + (1354 x 13.8%) = 0.69 + (186.852 (rounded down to 186.85)) = 187.54

Strangely however, this £0.04 difference in the employee contributions is always present, even when using a monthly value of £647.00 (£1 Employee NIable pay) should give an answer of £0.12 your calculator gives £0.16

The biggest issue however comes in your Student Loan calculation, for the same value of £2000.00 you calculate a SL contribution of £67.50 however it is not possible to have pence within Student Loans as the rules state all results are rounded down to the nearest pound.

Even without the pence issue however your calculation is £10 higher than expected. According to my calcuations the result is £57 as detailed below:

Annual SL Threshold £16365 therefore monthly threshold = £1363.75 (16365 / 12)

£2000.00 - 1363.75 = £636.25

636.25 x 9% = 57.2625 which rounds down to £57

I believe you are using a Student Loan annual threshold of £15000.00 which has not been in force since 2011/12 year.

Kind Regards,


2 Replies

Hello Peter, firstly apologise for the extremely late response. Design team don't venture into the community, but I wanted to come and thank you for the well thought out comment. You're right, the current Stanley income tax page is very out of date and we're looking to update the page to ensure we provide a good and accurate calculations in the very near future.

I'll forward your post to the team member in charge of the project, thanks again for taking time to post!

Hello Stanley,

I am just going through the Network and answering some outstanding queries.

You will be pleased to hear that we no longer use the information from Stanley calculators but base our figures directly from the HMRC calculators. The most common calculator and tool we use for our Open Payroll software is Basic PAYE Tools for RTI purposes.

The figures are highly accurate and account for the new tax years' personal allowances. The new tax year for 2014/15 is also based on this and is almost ready for valued Clearbooks customers such as yourself to use.

Thank you for your custom and continued patience as we make changes to our suites of software.



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