Savings goals
Package:
FINANCE_PACKAGE. Registered bycreateEngine(); for a slimmer engine, register it explicitly (see choosing packages).
A savings goal is the interest maths run backwards: instead of asking what a sum grows to, you ask how long it takes to reach a target, or how much you must put aside each period to get there in time.
how long to save <target> at <amount> <period> answers the time, and how much per month to save <target> in <duration> answers the contribution.
how long to save $10,000 at $500 monthly // 20 monthshow much per month to save $12,000 in 2 years // $500.00The interest-free forms are exact division. Add at <rate> and the money earns
interest on the way, so the goal arrives sooner or the monthly amount is smaller;
the rate compounds monthly.
how long to save $10,000 at $500 monthly at 12% // 19 monthshow much per month to save $12,000 in 2 years at 6% // $471.85The duration answers in the contribution’s own unit (weekly reads in weeks),
and the count rounds up, because a part period has not yet reached the goal. The
per-month form takes a duration in months or years, and there reach reads the
same as save; the how long to save form has no reach spelling. A
bare-number target answers a bare number.