As the deadline looms for completing self-assessment tax returns, more than half of self-employed Brits will be filing by the seat of their pants.

New kid on the tax block Zaptax said many self-employed people are "leaving it to the last minute or giving up on their returns altogether because they are simply too stressed, irritated or worried to continue". It added: "Due to this, self-employed people are at more risk of incurring the hefty fines and penalties imposed by HMRC or making mistakes which result in under- or over-payments."

There is no hiding place from the January 31 cut-off. If you forget, there is an immediate £100 fine, even if there is no tax due, and after three months a £10-per-day fine kicks in, up to a maximum £900.

Zaptax last month launched the first self-assessment tax app, and has surveyed 1270 people between the ages of 18 to 68 and spanning industries from beauty to construction to IT to accountancy to media.

More than half said they did not understand how to perform the self-assessment. After completing their returns, the majority said they felt "confused" (78%), "irritated" (73%) and "worried" (66%). Only 12% felt "confident" and 8% "relaxed" during the process.

Of those with negative feelings, more than half (57%) confessed that this had meant they left the task to the last minute. A further 23% said it had prevented them from filling the forms in properly or at all.

Nathan Evans, founder of Zaptax, said: "The self-assessment tax process as it stands is still too complex. People are working longer hours, often for little money, and they don't need this extra torture. We would also advise them, of course, to try out our app, instead of tearing their hair out while trying to go it alone. And if it turns out they actually do need an accountant then Zaptax will recommend one, and we don't charge them a penny."

HMRC said the most common online mistakes are: failing to complete all the pages you need to; completing the return but then failing to press the "submit" button; using punctuation or characters not allowed in online boxes; and submitting inconsistent numbers when calculating the tax due.

Meanwhile, accountants Baker Tilly has some reminders:

l Have your P60 and P11D (benefits) forms to hand as you'll need to use the precise figure for your income. If you're self-employed then you'll need your accounts or details of income and expenditure.

l If during the year you have received any "one-off" payments - such as for a short period of freelance work or from an investment that has matured - you will need to declare these. But remember to tick the box on your form so they are not included in your tax code in future.

l If you are a landlord you must declare your annual income from renting your property. You can claim mortgage interest, costs of repairs and maintenance and any other costs. If you let the property furnished, you can also claim a "wear and tear" allowance.

l From last year, parents who earn more than £50,000 a year and collect Child Benefit must complete a self-assessment return.