# Ledgerly Compound Growth Calculator

> What your savings grow to with monthly contributions, fees and inflation — year by year. Compound interest with a starting amount, monthly contributions (at the start or end of the month, with a yearly raise), monthly, yearly or daily compounding, yearly fees and inflation. Shows the final balance, the same in today’s money, how much you paid in, how much fees cost including the growth they take away, the doubling time and a year-by-year table. Part of Ledgerly’s Debt & Growth.

Part of usefulweb.app (https://usefulweb.app/). Part of [Ledgerly](https://ledgerly.usefulweb.app/) (ownerApp: ledgerly). Results are deterministic calculations from the inputs and the listed assumptions; the API returns exactly what the web page shows.

## Use it
- Human interface: https://ledgerlycompoundgrowth.usefulweb.app/ (interactive tool at https://ledgerlycompoundgrowth.usefulweb.app/tool)
- JSON API: POST https://ledgerlycompoundgrowth.usefulweb.app/api/v1/calculate with a JSON object of inputs (schema: https://ledgerlycompoundgrowth.usefulweb.app/api/v1/tool)
- OpenAPI: https://ledgerlycompoundgrowth.usefulweb.app/openapi.json
- MCP (Streamable HTTP): https://ledgerlycompoundgrowth.usefulweb.app/mcp - tool `ledgerly_compound_growth`

## Inputs
- currency (text): Currency - ISO code used for the labels, e.g. EUR, USD, GBP.
- startAmount (number): Starting amount
- monthlyContribution (number): Added every month
- contributionTiming (select): Added at the
- contributionIncreasePercent (number): Raise of the monthly amount (% per year)
- years (integer): Years
- annualReturnPercent (number): Return (% per year, before fees)
- compounding (select): Compounding
- feePercent (number): Yearly fees (% of the balance) - Fund costs (TER), platform or advice fees, charged monthly on the balance.
- inflationPercent (number): Inflation (% per year) for today’s money

## Method
- Month by month: a contribution at the start of the month (if chosen), growth at the monthly rate, the fee (yearly percentage ÷ 12 of the balance), then a contribution at the end of the month (if chosen).
- Monthly rate: rate ÷ 12 for monthly compounding, (1 + rate)^(1/12) − 1 for yearly compounding (the same yearly result), (1 + rate/365)^(365/12) − 1 for daily compounding.
- The monthly contribution rises by the yearly raise at the start of every new year. Today’s money divides the balance by (1 + inflation)^years.
- Lost to fees = the balance without fees minus the balance with fees: the fees themselves plus the growth they would have earned. Doubling time = ln 2 ÷ ln(1 + return after fees); the rule of 72 is shown for comparison.

## Limits
- Returns are not guaranteed and change from year to year; this model uses one constant rate. It is not investment advice.