Compound Interest Calculator

This calculator estimates the growth of your savings or investments using compound interest with optional recurring contributions. Enter your initial amount, annual rate, compounding frequency, and time horizon; then add monthly or yearly deposits and choose whether they happen at the beginning or end of each period. The results prioritize clarity on mobile: a large Future Value figure appears first, followed by a concise Totals block and a compact yearly Snapshot. You can also download a clean CSV for spreadsheets.

Accurate inputs make the output meaningfully useful for planning. Use a realistic annual rate based on your account type or long-run expectations; conservative assumptions help avoid over-promising. Choose the compounding frequency your bank or broker uses—many savings accounts compound daily, while some products compound monthly or quarterly. If your deposits are automated, select monthly. For ad-hoc contributions, yearly can be easier to plan. The beginning vs. end toggle reflects cash timing: contributions at the beginning of the period earn interest longer and slightly lift the final result. If you expect irregular deposits, consider modeling the typical amount here and holding a buffer in your timeline rather than assuming perfect consistency.

• Currency: the tool auto-detects a likely currency but you can override it anytime.
• Inflation: add a yearly inflation rate to see future value translated into today’s money; this is helpful for long horizons where purchasing power can drift.
• Time horizon: longer holding periods amplify compounding, and even small recurring deposits can snowball over decades.

The top line shows your projected Future Value. The totals summarize Total contributions, Total interest earned, the effective APY, and your Compounding choice. If you entered inflation, you’ll also see an inflation-adjusted future value to gauge real purchasing power. The snapshot card provides a simple pulse check at Year 1, Year 5, a midpoint, and the final year, including what you contributed and how much interest accrued in each of those years. Use these touchpoints to sanity-check progress without scrolling a long table and to decide when to step deposits up or down.

Treat these numbers as planning guides rather than promises. Markets fluctuate, rates change, and fees or taxes can alter your path. The goal is to map a trajectory, track progress, and adjust deposits or time horizon rather than fixate on a single outcome. If results look unrealistically high, dial the rate down, shorten the compounding frequency to monthly, or add inflation so you’re comparing like-for-like in today’s terms.

For steady growth, many savers automate deposits and revisit the plan a few times per year. If rates rise, you can increase deposits or shorten the time to a milestone; if rates fall, you can extend the timeline or raise contributions. Diversification, fees, and tax wrappers also matter—this tool keeps its scope tight to show the core compounding effect cleanly. It does not model variable returns, irregular deposit gaps, or tax treatment; keep that in mind when comparing account types. When you need finer control, export the CSV, add columns for taxes or fees, and test “what-ifs” in a spreadsheet.

As a rule of thumb, prioritize consistency: a modest monthly deposit started early typically beats a larger, later lump sum. Small tweaks in timing—like switching from end-of-month to beginning-of-month contributions—have a measurable impact over long horizons because each deposit earns interest for more periods. Re-run the plan after bonuses, windfalls, or life changes to keep your path aligned with the goal you care about.

The calculator converts your nominal APR and compounding frequency into an effective monthly rate, then simulates month by month so deposits and timing are applied consistently. We also compute an effective APY—the return you’d earn over a year after compounding. If you enter inflation, we discount the final balance to show an approximate value in “today’s money.” Taxes, fees, penalties, and changing rates are outside this scope so the projection stays easy to compare across accounts.