Savings Plan Calculator - Compound Interest Growth

The savings plan calculator projects how a monthly deposit and an optional opening balance grow when interest compounds monthly. People use it to test a down-payment fund, an emergency reserve, a wedding budget, or a cash sleeve inside a brokerage account. The engine converts the annual interest rate you enter into a monthly rate r = i/12 and a month count n = years × 12, then adds two standard future-value pieces: the compounded lump sum and the ordinary annuity of end-of-month deposits. Future value of the starter balance is PV × (1+r)^n. Future value of the deposit stream is PMT × ((1+r)^n − 1)/r when r is not zero, or simply PMT × n when the rate is zero. Modeling deposits at period-end matches how many banks post interest and how an automatic transfer often lands after payday. Daily compounding, quarterly credits, or a mid-month deposit will move the statement a little, so treat the figure as a planning projection rather than a contract. A common use is comparing a 4% high-yield savings account with a slightly higher conservative bond fund over the same monthly transfer. Another is checking whether raising the deposit after a raise shortens the wait for a goal, or whether a few thousand dollars of seed money matters more than another year of waiting. Because the savings plan calculator ignores taxes, account fees, contribution caps, and inflation, the displayed balance is a nominal ceiling. A $50,000 future value is not automatically $50,000 of today's spending power. Promotional APYs are a frequent trap. A teaser rate that lasts three months should not be projected for ten years. Variable rates, step-up CDs, and employer matching sit outside this model. Keep the currency consistent, run a conservative case and an optimistic case, and write down the inputs so you can repeat the scenario after a rate change. The result is an educational estimate for household planning, not personalized investment, tax, or legal advice, and it cannot replace the terms of a bank product or the judgment of a licensed adviser.