Put the same money in each account type and see how the assumptions play out. The four ISA wrappers are tax-free; the General Investment Account is the taxable comparator — the difference between them is the tax an ISA saves you. Edit any assumption; everything recomputes live.
Illustrative model, not advice. 2025/26 tax figures (verified, but they change): dividend allowance £500; dividend tax 8.75% / 33.75% / 39.35% (basic / higher / additional); CGT annual exempt £3,000; CGT on shares 18% (basic) / 24% (higher & additional). Simplifications: dividends are taxed annually and net-reinvested; the GIA's capital gains are realised once at the end of the horizon with a single £3,000 exemption (in practice you could use the exemption each year by harvesting, reducing the drag); the dividend and CGT allowances are modelled in isolation per account, ignoring interaction with your other income and the band-straddling stacking order; the Cash ISA's comparator (taxable cash interest, personal savings allowance) is not shown — the GIA here holds investments. The LISA accepts a maximum £4,000/year and carries a 25% penalty on non-qualifying withdrawals (not modelled in the net figure). Defaults are plausible placeholders — change them above.