Can I ask for feedback on a Self Assessment calculator I’ve built?

[GinTonicRemoteControl]

Hi,
I’ve built a self assessment tax calculator (on a long-haul flight to Australia) and would love to get some feedback but I wanted to check first if it’s okay to post about it here?
I put it together after getting frustrated with the HMRC version which can be a bit cumbersome to use and also the free online ones are quite limited, especially if your income includes things like salary sacrifice, pensions, interest, dividends or marriage allowance.
My aim was to make something clearer and more flexible and it would really help to get some real-world feedback from people who actually do a self assessment.
I suppose its a question for the community and the moderators - is it okay to post the link here for some feedback as I can see we have some people in the forum who know quite a bit about income tax?

Go for it!

As long as you list all constraints on the version where you hosting it you'd find a lot of people happy to test it for you. If it is a spreadsheet ppl will forward it to others without what you've written in your post.

https://taxgrid.co.uk
Thank you timestressed for your response. Including the constraints is a great suggestion and I have added a “what’s included” and “what’s not included” section to the website. I have not had previous experience launching a website and its been a steep learning curve. The website is very new and I want it to be a free calculator so I did activate some low level google ads last week (which shouldn’t affect the usability) to help offset some of the hosting costs – hope that doesn’t detract…

The website focuses purely on the income tax self-assessment calculation so it excludes:

• capital gains tax, child benefit high income charge, student loans, national insurance, details BIK calculations and any payments towards the tax total for the year (including tax codes). The website also excludes Scottish tax, but I will build that in in the future depending on whether I can get the basics of this one correct.

The website includes:
3 types of income namely non-savings/ non-dividend, savings interest and dividends with built in tax rates and allowances for the last 4 years.
The website has built in allowances for savings interest, starter rate of interest and dividends.
There are limit checks, reductions and warnings for pension contributions, personal allowance taper and tapered pension annual allowance when income exceeds £260k and marriage allowances that do not meet the requirements.
There are additions and reductions to personal allowance for blind person’s and marriage allowance and I have included marriage allowance donated and received.

Known limitation:
There is automatic personal allowance allocation reordering but only “all or nothing” between savings and dividend when the personal allowance is not fully utilised by salary. The calculator has no optimisation to run all iterations to achieve the minimum tax possible when allocation of personal allowance between salary, savings and dividends as that beyond my basic coding skills. Also, only calculates in-year total tax, so if you have amounts claimed from prior years etc, they have not been accommodated.

I think I am aiming to cover 90% - 95% of typical scenarios so that it’s a useful estimating tool to help people understand how the tax band interact with each other.

Hi, Interesting, where might I put in my tax code, and any extra lines for bonuses etc? Thanks

Thanks for taking the time to comment, much appreciated. Great point on the bonus - I've added that as a separate line now to save people having to combine it on the salary line.
On tax codes... I haven’t included them because the calculator is focused on working out your total income tax for the year rather than how it’s collected through PAYE but super helpful you mentioning that, as I think I need to be clearer that it attempts to mirror the self assessment process but you certainly wouldn't be alone wondering where to input your tax code.

Many thanks GinandTonic, it’s a lot of work and looks very good. Will be nice to be able to use and see where the taxes might land, particularly given a surprise tax bill very recently.

Rental income - remember the limit on mortgage interest relief

I just use the form on the Self assessment Government Gateway
Seems straight forward
Just fill in the boxes

Thanks for taking the time...
Yip, good spot. I did get a bit lazy in the rental section and didn't have many input options but I've added additional input boxes and the calculation now deducts the mortgage interest relief.

So by way of example:
Gross salary 30,000

Gross rent 12,000
Deductible expenses 2,000
Net Rental Income 10,000

Mortgage interest 5,000

You are going to have income tax of £4,486 (£5,486 less £1,000 of mortgage interest).

So, why recreate a calculator that already exists online?

I've asked myself that question many times - I think because I'm a sucker for a challenge and I couldn't find a calculator (outside of HMRC) that actually included all the income types. There are lots of net pay and salary calculators out there that focus on employment income but I couldn't find one that just did annual income tax that showed the visibility into the numbers I was looking for to plan ahead for things like private pension contributions etc.

I'll admit that I haven't actually looked at the website (so this question might be answered there) but what liabilities are you opening yourself up to? If someone relies on your calculation and it turns out to be wrong, can you be sued? Do you have caveats in place?

I have similar disclaimer wording that the Money Saving Expert calculator has about being an estimate and not financial advice etc.

Grateful as always for feedback.
I've added the High Income Child Benefit Charge HICBC to the calculator so you can see the impact of salary sacrifices or pension contributions on the charge.
Let me know your thoughts?
taxgrid.co.uk