Flybird2023

I made 12000 gain in 2020-2021, and 16000 loss in the same year. After reading thread here, my understanding to the gain and loss rule is: £12000 gain is less than 12300 allowance. so no tax to pay. £16000 loss can be carried forward for future to use. If I have made £12400 gain instead, I can carry forward £15900, as £100 is used to offset the gain to £12300. Am I right? If I have filed tax return online at the time of 2021 for the tax year 2020-2021, can I still claim above loss now? If so, should I use SA108 in writing with supporting documents or something else? Thanks!

I have made £24000 gain in 2019/20, and £15000 loss. My understanding is that I can report £3000 loss for that year, as 15000 - (24000 - 12000) = 3000 Can I still report this loss or it is too late?

I didn't realize I have made gain after loss over £12300 in 2020-2021 tax year, as the stock market was really bad in 2020, I am still in a big loss overrall right now. So I made loss in 2021-2022, 2022-2023. I have filled online form to register for self assessment on 4th OCT, but has yet received my UTN. What should I do now to report those gain and losses?