Junior SIPP Growth Calculator

The calculator converts the expected annual return and inflation rates into monthly equivalents and applies them over the total number of months from current age to end age. It separately grows the starting contribution for the full period and then adds the future value of all monthly contributions as a stream of deposits. Finally, it deflates the nominal projected pot by inflation to estimate the value in today’s money, and splits the difference into “total contributions” versus “investment growth.”

The model assumes a constant annual return and a constant inflation rate, with smooth monthly compounding—real market returns are not constant. It also excludes fees, provider charges, taxes, and Junior SIPP-specific government rules (like eligibility and contribution limits), so actual outcomes may be lower or follow different timing. If the expected return is close to the inflation assumption, small input changes can noticeably affect the “real growth” (today’s money) result.

If your expected annual return is less than or equal to inflation, purchasing power may not increase meaningfully, and the calculator will flag this as real returns being negative. Make sure the end age is greater than the child’s current age—otherwise the projection can’t be computed. Treat the output as an illustrative estimate, not financial advice; for planning, consider using multiple scenarios and discussing assumptions with a qualified adviser.

If the child’s current age equals or exceeds the end age, the calculator returns zero growth and flags the inputs as invalid for projection. If you enter zero monthly or zero starting contributions, the pot will still accumulate only from what you’ve contributed (or remain at £0 if both are £0). Inflation set to 0% will make nominal and today’s money values match, while very high inflation relative to returns will significantly reduce the inflation-adjusted result.