In short

  • Subtract the future value of current savings before solving for new deposits.
  • A longer timeline or higher assumed return reduces the mathematical monthly requirement.
  • The required amount is a planning estimate, not a promise of investment performance.

Work backward from the target

A savings-goal calculation asks a different question from a growth projection. Instead of choosing a deposit and calculating the ending balance, it starts with the desired ending balance and solves for a fixed monthly contribution.

Account for existing savings first

The current balance may grow during the saving period. The formula subtracts that projected future value from the goal, then spreads the remaining requirement across the contribution stream.

Rate, time and timing all matter

More months create more deposits and more time for compounding. A higher assumed rate lowers the calculated deposit, but also adds uncertainty. Beginning-of-month contributions receive one additional month of growth compared with end-of-month contributions.

Example monthly requirement

Starting with $10,000 and targeting $100,000 in 10 years at a nominal 5% compounded monthly requires about $537.92 at each month-end. At a zero rate, the remaining goal is simply divided by the number of months.

Plan for real-world variation

Rates, income and expenses can change. Revisit the calculation periodically and keep fees, taxes, inflation, emergency liquidity and potential investment losses outside the headline estimate.

Sources

These primary or official references support the formulas, definitions or scope used in this guide.