How much to save each month
This is the reverse of a compound interest calculation. Instead of asking "if I save X per month, what will I have?", it asks "I want to have this much by a certain date — how much must I save each month?". With no interest, it is just the amount still needed divided by the number of months. With an interest rate, part of your goal is met by growth, so the required monthly amount is lower.
Why the interest rate matters
Money set aside in an interest-bearing account or investment grows over time, so you don't have to contribute the full target yourself. The higher the rate and the longer the horizon, the more of your goal is covered by compounding and the less you need to save from your own pocket each month. Leave the rate at 0 for a plain savings plan with no assumed return.
Turning a goal into a habit
Breaking a large target into a fixed monthly figure makes it manageable and easy to automate. A 20,000 goal in five years with no interest is about 333 per month; add a 4% return and the monthly figure drops noticeably. Recalculate whenever your timeline, starting balance or expected return changes.
Frequently asked questions
Does this assume monthly or annual contributions?
Monthly. The result is the amount to set aside each month, and any interest rate you enter is applied monthly (annual rate divided by twelve) with contributions compounding over the full period.
What if I've already saved some money?
Enter it in the "Already saved" field. That starting balance also grows at the interest rate you set, reducing the monthly amount you still need to add.