Two questions, answered both ways round. Put in a monthly amount, a term and an interest rate to see what you end up with, or name a target amount and a deadline to see what you need to save each month to get there.
Most savings planning is one of two calculations. Either you know what you can put aside and want to know where it gets you, or you know the target and need the monthly figure. They are the same formula rearranged, and both are here.
Saving 200 a month from age 25 to 65 at 5% produces more than saving 400 a month from 45 to 65, despite the second person contributing the same total. The difference is time in the market, not discipline. If you cannot save much yet, starting small still beats waiting.
Contributions land at the end of each month, the return is constant, and nothing is withdrawn. Real returns are volatile, and sequence of returns matters if you are drawing down. Treat this as a planning aid rather than a forecast.
A common rule of thumb is 20% of take-home pay towards saving and debt repayment, but the useful number is the one you can sustain. Consistency over years matters far more than the rate in any single month.
Contributions are applied at the end of each month, after that month's interest. This is the conservative assumption and matches how most savings accounts credit deposits.
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