Solving backward from a target
This goal calculation first grows the current balance to the deadline, then solves for a level end-of-month deposit that closes the remaining gap. It is the future-value form of an ordinary annuity. The method assumes every planned deposit is the same size and earns interest from the month after it is made.
Worked five-year goal
The default target is $30,000 in five years. Starting from $5,000 at 4% annual interest, the existing balance grows to $6,104.98. The remaining target is not simply divided by sixty because new deposits earn interest too: the required monthly contribution is $360.41.
The date drives the payment
A deadline is part of the formula, not a motivational label. Moving the date earlier increases the required deposit sharply because there are fewer deposits and fewer months of growth. If pay arrives biweekly, convert the schedule deliberately; a monthly contribution assumption can hide a cash-flow mismatch even when the annual total is the same.
Test the target itself
Test the target against what it must purchase. A $30,000 house deposit, tuition bill, or reserve may change with prices before the chosen date. When the target has a fixed invoice amount, the model is clearer; when it is a future purchase, run an inflation-adjusted target rather than treating today's price as settled.
Irregular saving needs a schedule
This page does not model account withdrawal restrictions, tax, irregular windfalls, changing yields, or a missed contribution. It also cannot tell whether a target is affordable relative to debt or essential expenses. If deposits vary, use a dated cash-flow plan and treat this level-payment answer as a reference point.
Update the live plan
Review the plan after every material change in balance, deadline, or rate. The record to keep is the target date, current account balance, and recurring transfer amount, not just the headline deposit. That makes an updated estimate explainable when the deadline approaches.
A missed-month test
Run the calculation with one fewer year or a slightly larger target before setting an automatic transfer. That shows whether the plan has room for a missed month, or whether the deadline depends on every contribution arriving exactly as scheduled.
Target achieved early
When the current balance and planned deposits would exceed the target before the deadline, the required monthly result becomes zero. That is a signal to choose what happens to later transfers: stop them, redirect them, or raise the target. Leaving an automatic transfer running is a different plan from merely reaching the first target date, and the calculator cannot infer that choice.
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It is an educational estimate, not financial, tax, or legal advice.