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Savings Goal Calculator

Solves for the fixed end-of-month deposit required to grow current savings to a goal amount within a given number of years at a monthly-compounded annual rate.

When to use

You know the target amount, the deadline and an expected return and want the monthly saving required (emergency fund, down payment, tuition).

Do not use when: You already know the deposit and want the resulting balance (use compound-interest or future-value), or the contributions are irregular.

Formula

i = annual_rate_percent / 1200; m = 12·years; FV_current = current_savings × (1 + i)^m; monthly_deposit = (goal_amount − FV_current) × i / ((1 + i)^m − 1); if i = 0, monthly_deposit = (goal_amount − FV_current) / m

Ordinary-annuity (end-of-month) sinking-fund formula with monthly compounding; returns are assumed constant and taxes and fees are ignored.

Inputs

Parameter	Type	Unit	Required	Description
`goal_amount`	number		yes	Target balance to reach. Range: > 0, ≤ 1000000000000
`current_savings`	number		default 0	Amount already saved; it keeps compounding at the same rate. Range: ≥ 0, ≤ 1000000000000
`years`	number	years	yes	Years until the goal is needed; rounded to whole months. Range: > 0, ≤ 100
`annual_rate_percent`	number	%	default 0	Expected annual interest or return in percent, compounded monthly. Use 0 for cash under the mattress. Range: ≥ 0, ≤ 100

Outputs

Output	Type	Description
`monthly_deposit`	number	End-of-month deposit that reaches the goal exactly.
`months`	integer	12 × years, rounded.
`total_deposits`	number	monthly_deposit × months.
`future_value_of_current_savings`	number	current_savings × (1 + i)^months.
`interest_earned`	number	goal_amount − current_savings − total_deposits.

Example

50,000 in 10 years at 5 %: {"goal_amount":50000,"years":10,"annual_rate_percent":5} → {"monthly_deposit":321.99,"months":120,"total_deposits":38639.31,"interest_earned":11360.69}

20,000 in 3 years starting from 5,000 at 4 %: {"goal_amount":20000,"current_savings":5000,"years":3,"annual_rate_percent":4} → {"monthly_deposit":376.19,"months":36,"future_value_of_current_savings":5636.36}

GET https://tttkmbb.com/api/v1/calculate/savings-goal?goal_amount=50000&years=10&annual_rate_percent=5

Machine access

API: GET https://tttkmbb.com/api/v1/calculate/savings-goal (query parameters) or POST with a JSON body {"inputs": {...}}
Schema: https://tttkmbb.com/api/v1/calculators/savings-goal · Markdown: https://tttkmbb.com/finance/savings-goal.md · JSON definition: https://tttkmbb.com/finance/savings-goal.json
MCP: server https://tttkmbb.com/mcp, tool run_calculator with calculator_id="savings-goal"
OpenAPI operationId: calculate_savings_goal_deposit
Freshness: static. Authentication: none. Rate limit: fair use (see rate limits).

Sources

Wikipedia – Time value of money (reference)
Investopedia – Compound Interest: Formula and Examples (reference)

FAQ

What if my current savings already cover the goal?

monthly_deposit is reported as 0 and a note says the existing balance reaches the goal on its own at that rate.

Should I use a nominal or real return?

Use a nominal return if the goal is a fixed nominal sum; use a real (inflation-adjusted) return if the goal is in today's purchasing power (see inflation).

Related calculators

Compound Interest Calculator — Project the balance for a chosen deposit instead.
Inflation Calculator — Convert a goal in today's money to its future nominal cost.