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Make calculating tax easy for self employed people

Triginta is an online bookkeeping tool with a unique tax calculator designed for the needs of self employed people.

You can use the tool to get an instant calculation of your tax and National Insurance for the year to date.

Then you can update your invoices and expenses as you go

  • Create invoices online and input the figures automatically into your books
  • Track payments and income
  • Record your expenses as you go and input the figures automatically into your books
  • Snap and save receipts and link them to your claims
  • Get an accurate calculation of how much you should set aside for tax and NI each month
  • Build up a clear picture of your self employed finances through the year
  • Easily transfer your figures into your self assessment return at the end of the year

Normal membership costs £23.88 a year (after three months trial) but for a limited period you can get Triginta’s great features FREE.

Click below to get your free membership. You can start by entering your income and expenses for the year to date and then sign up for your free membership.

See how it works...

We're here to help you


The rules around being self employed can sometimes be confusing. We're here to help


Check out our guide to self employment

Compare Triginta Features

Triginta Open Access Triginta Subscription
One-off tax calculation
Guide to self employment
Create invoices
Track invoice payments
Record expenses as you go
Snap and save receipts
Detailed tax calculation as you go
Input employment income into tax calculation
Input pension contributions into tax calculations
Easily transfer figures into Self Assessment return
FREE £1.99 / month
Free for the first 3 months

Why I created Triginta

I created this site after being self-employed myself and developing a set of tools that I thought could be useful for other self-employed people. I hope you’ll find it meets your needs and I would welcome your comments and feedback so I can keep it relevant.

I have looked around other sites that offer book-keeping tools – I’d encourage you to look at them too – and concluded that they were offering too many features that weren’t relevant for the vast majority of self-employed people and they were overpriced for the value they could provide for the average freelancer.

I was well into my career when I became self-employed. I was already doing my own self-assessment tax return, I was familiar with accounts procedures and I was pretty savvy with spreadsheets. I decided I didn’t need an accountant and I could set up all the necessary procedures and customised spreadsheets myself.

I created my own invoicing and expenses procedures and integrated them into an accounts package that kept everything organised and meant that if I had the dreaded visit from HMRC I could show them exactly where I stood. As I was registered for VAT, I did the same thing to track my VAT receipts and payments.

One thing I knew I needed from day one was an accurate way of calculating how much tax and NI to set aside every month. I wanted to set aside the right amount each month – enough to be sure I was covering what was need but not too much either. But more than anything it was the peace of mind of knowing I was on top of my outgoings and liabilities.

I had been used to the PAYE system from when I was an employed person and I wanted to have something close to that. I didn’t want something that just projected an average for the year; there are plenty of those online but they’re not much use until the year is already over. I wanted a system that told me exactly how much tax and NI to deduct from my earnings that month, taking account of variations in my income and how much of each tax band I had used up for that month.

The calculator served me well, and when I came to submit my tax return the result that HMRC came up with was invariably within a few pennies of what I had already set aside.

None of this is massively complicated but it did seem to me that it could be helpful to other self-employed people. When I looked at the other book-keeping sites they did look very over-engineered and not really relevant to the needs of the vast majority of self-employed people with pretty straightforward circumstances. And they were very pricey, even for their entry-level products.

So I’ve deliberately tried to keep it simple – and therefore cost effective which is reflected in the pricing. But if you think I’m missing anything important, or you have any comments to improve the site, please let me know on admin@triginta.co.uk

First Three Months FREE

It’s free to use the calculator. Then if you want to benefit from the full Triginta features you can sign up free for the first three months. That means you can get an instant calculation of your tax and NI for the year to date. And you can start to use Triginta to record your invoices and expenses, building up a clear picture as you go of how your self employment finances are developing.

After that it’s just £1.99 a month. There’s no fixed contract so you’ll be free to opt in or out whenever you want.

Not only will you be able to keep on top of your tax and NI every month, all your invoices and expenses will be in one place so that you’ll have them at the end of the year.

All you have to do is enter your turnover in the year to date and your expenses, along with some basic information about you to enable us to get the calculations right for you.