CopperCoil

CopperCoil is a compound interest calculator built for anyone saving toward a real goal — retirement, a house down payment, a college fund, or just an emergency cushion. Instead of a bare formula, every ledger you create turns into a living growth chart that redraws itself the instant you touch a number, so compounding stops being an abstract idea and becomes something you can actually watch happen. Open the app and you land on your workspace: one ledger, one chart, and four tactile controls — a starting-amount stepper, a coin jar you fill for your monthly contribution, a return-rate dial, and a term scrubber for how many years you're saving. Drag any of them and the projection curve redraws live, along with the projected final balance, in your own currency. Tap a point on the curve for a year-by-year breakdown of principal, contributions and interest earned. Log real deposits, withdrawals and interest credits against a ledger and the chart overlays your actual balance against the forecast, so you can see at a glance whether you're ahead of or behind plan. KEY FEATURES ✓ Compound interest calculator — starting amount, monthly contribution, annual return and term, compounded yearly, quarterly, monthly or daily ✓ Live growth chart — a compound-growth curve that redraws instantly as you adjust any input, with milestone markers at $10K/$50K/$100K/$250K/$500K/$1M ✓ Multiple savings ledgers — retirement, a house, college, emergency fund or any custom goal, each with its own currency, icon and colour ✓ Ten ready-made goal presets — retirement, first-home, college fund, emergency fund, FIRE, and more, pre-filled with sensible starting numbers ✓ Transaction log — record real deposits, withdrawals and interest credits and compare your actual balance against the projection ✓ Compare mode — put up to three ledgers side by side and see exactly how much higher or lower one ends up against another ✓ What-If studio — scratch-test any ledger's numbers on a throwaway copy, with both projections overlaid, before committing to a real change ✓ Retirement withdrawal calculator — enter a nest egg and a withdrawal rate to see how many years it lasts, with a one-tap 4% "safe withdrawal" rule ✓ Rate reference — typical historical return ranges for bank deposits, bonds, index funds, real estate, crypto and more, with a one-tap "use this rate" ✓ Inflation-adjusted and after-tax views — see what a projection is really worth in today's money or after your marginal tax rate HOW IT WORKS 1. Pick a starting point — a ready-made goal preset, a blank ledger, or the built-in sample ledger to explore first. 2. Set your four numbers — starting amount, monthly contribution, annual return and term — and watch the growth chart update live. 3. Log real activity as it happens, or open the menu for compare mode, the retirement calculator, What-If studio or the rate reference. WHY COPPERCOIL — the whole app runs on your device. There's no account to create, no server to talk to, and nothing to sync. Every calculation happens instantly and locally, so it works the same on a plane as it does at home. The interface is built to be touched, not just read: drag a dial, drop a coin in a jar, scrub a timeline — the numbers and the chart move with you. PRIVACY — CopperCoil works fully offline. There is no account, no ads, no tracking, and no data ever leaves your device.