A single ISA account on the surface — one balance, one deposit, one withdrawal. Underneath, the platform runs four ISA wrappers, tracks the shared £20,000 allowance, and uses a peer-funded pool to make most withdrawals instant. Watch both sides at once.
This is a concept toy, kept deliberately simple and honest. A real build would have to handle all of the following — several of them are hard statutory limits, not design choices:
The same goal — saving tax-efficiently across ISA types — handled the way it works today versus the way OneISA handles it.
First-pass contrast for illustration — the “old world” reflects typical provider behaviour, not any single competitor.
The same money, two points of view: what you earn each year, and what OneISA makes from you. These move as the balances above change — deposit, withdraw, cross the tax year, or switch on IFISA lending and watch both sides shift.
Illustrative annual snapshot on current balances (reinvested, no withdrawals assumed). Rate assumptions: S&S 6.5%, cash 3.5% to you, IFISA lender yield 6.8%, platform cash margin 1.0%, S&S fee 0.25%, lending spread 1.5%. When IFISA lending is on, ~15% of your cash buffer is treated as lent through the pool. The "cash margin" is the same mechanism that can incentivise keeping money in cash — a tension we model openly. For a fuller model with adjustable assumptions and a multi-year projection, see the separate economics page.
The demo proves the core: one account, four wrappers, goal-driven routing, and a peer-funded liquidity engine. These are the next features — each either deepens trust or extends reach.
Illustrative figures throughout, at a small-fintech scale. Built to explore an idea, not to give financial advice. ISA rules verified against 2025/26 guidance; rules change.