🎯 Savings Goal Planner

It uses the standard future-value-with-contributions formula: FV(t) = P·(1+r)^t + PMT·(((1+r)^t − 1)/r), with monthly compounding. P is your starting balance, PMT your fixed monthly contribution, r the annual return divided by 12, and t the number of months elapsed. The simulator evaluates this month by month up to 600 months (50 years) and finds the first month where FV(t) is at least your goal.

The chart shows the growth curve rising toward — but never touching — the dashed goal line, and a message explains that the goal wasn't reached within the horizon. In practice this means the combination of contribution and return rate is too low for the target; increasing the monthly contribution almost always closes the gap faster than waiting for a higher return.

Because contributions add up linearly while a larger balance still compounds, doubling PMT typically more than halves the time to reach a goal — try it with the Slow & Steady preset and then bump the monthly contribution slider up. The effect is strongest early on, before the compounding on your existing balance has grown large enough to dominate.

For goals many years away, monthly contributions usually dominate because they accumulate every month; for goals only a few years away, a larger starting balance matters more because there isn't enough time for monthly additions to compound significantly. Compare the House Deposit and Aggressive Saver presets to see both effects.

Ten percent a year is already an optimistic long-run average for a diversified stock portfolio; savings accounts and cash ISAs in the UK typically sit well below that. The slider is capped at 10% to keep the model realistic — treat anything above roughly 5–6% as an equities-style assumption rather than a guaranteed savings rate.