ISA Calculator

Starting ISA value used as your compounding baseline from period one. Compounding is path-dependent, so a materially wrong starting balance can distort long-horizon outcomes and lead to poor contribution decisions.

Planned contribution amount in monthly or yearly cadence mode. This is usually your highest-control lever for progress, so set a value you can sustain rather than an optimistic number that may break after a few months.

Switch between monthly and yearly contribution planning behavior. Cadence affects allowance interpretation and planning rhythm, so ensure contribution amounts are equivalent when comparing scenarios.

Number of years used for forward projection. Horizon length changes sensitivity to return and inflation, so keep timeline consistent when comparing options.

Annualized growth assumption before inflation adjustment and volatility stress. Even small changes compound strongly over time, so use a conservative baseline and only then test optimistic variants.

Reference benchmark used to seed inflation assumptions with published data. This improves consistency over time and avoids purely arbitrary assumptions.

Near-term inflation assumption for the initial projection horizon. This can materially change real return in early years, especially when inflation is volatile.

Outer-year inflation assumption used beyond the short-term horizon. Long-run purchasing power is highly sensitive to this value, so review it as part of annual planning updates.

Estimated end-period nominal value under current assumptions. This is the headline figure most users check first, but it should always be read alongside inflation-adjusted value.

Total capital personally added over the full projection period. This helps separate plan quality driven by savings discipline versus market assumptions.

Projected return component above contributed capital. Use this to understand how dependent your plan is on market conditions rather than contribution effort.

Estimated purchasing-power equivalent of the end value. This is usually the most practical figure for future lifestyle planning.

Illustrative annual and monthly drawdown estimate from projected end value. Treat this as a rough planning signal rather than a guaranteed income rule.

Distribution width assumption for annual market returns in simulation. Higher volatility increases both downside and upside spread and changes planning confidence.

Distribution width assumption for annual inflation paths. This materially affects real-value downside risk in long-horizon planning.

Assumed co-movement between return and inflation in simulation paths. Correlation changes how frequently difficult market and inflation conditions happen together.

Conservative/base/optimistic percentile outputs from simulated paths. Use these as planning bands for cautious, expected, and stretch outcomes.

Short orientation text explaining what this summary area contains. It helps users remember this panel is a synthesized estimate view.

Summary of advanced tools including stochastic modelling and deeper controls. This should communicate user outcomes, not only feature names.

Contribution amount currently consumed within annual allowance. This is a hard constraint check before increasing contribution assumptions.

Unallocated contribution capacity for the current tax year. Use this to manage planned top-ups and avoid over-limit assumptions.

Indicator showing remaining allowance headroom or over-limit status. It provides an immediate go/no-go signal for contribution assumptions.

Selected year snapshots showing value, contributions, and growth mix. These milestones help users judge trajectory quality rather than only final-year outcomes.

Cross-matrix of return and inflation offsets to compare real-value outcomes. This is one of the best tools for resilience testing against macro uncertainty.

Reminder that results are illustrative estimates and not financial advice. Use it as a final interpretation check before acting on any projection.