You don't enter your tax code into TaxCalc.
Your PAYE tax code is provided by HMRC to your employer or pension provider, in order to work out how much tax to take off your pay each month. This should mean that the correct amount of tax is collected from your pay throughout the tax year.
Your tax code is based on your personal allowance, which is then adjusted for other items like estimated pension contributions or any benefits you receive. If these adjustments are estimated correctly and your circumstances do not change during the tax year, you won't have any additional tax to pay at the end of the year.
PLEASE NOTE: The tax code does not affect the amount of personal allowance available to you and there is nowhere on the tax return for you to alter your personal allowance.
At the end of the tax year HMRC and TaxCalc take your actual income and benefits received and deduct your personal allowances to work out how much tax you should pay – or how much should be repaid to you. Because this calculation looks at the actual income and expenses, you don't need to enter your tax code in TaxCalc. However, you may need to enter some of the figures used by HMRC in the calculation. Please see the instructions below on where to enter this on the 2018-19 return.
SimpleStep Mode: Browse to Working out your tax. The adjustment needs to be declared in the section for Underpaid tax for earlier years included in your tax code for 2018-19. Note if this box is yellow in colour, you need to tick the top box for Do you currently have any income taxed under PAYE?
HMRC Forms Mode: Tax Calculation > Page 1 > Box 7.