Lumpsum Calculator

Lumpsum Calculator takes a single amount invested once and works out what it becomes. There are no further contributions, so the whole of the growth comes from compounding on the original sum, which makes it the clearest demonstration of what a rate of return actually does over time.

Compounding frequency is a real input rather than a detail. The same twelve per cent compounded monthly rather than yearly produces a noticeably larger result, because each month's growth starts earning in the next. The effective annual rate shown in the message is the honest comparison figure: it is what the quoted rate is really worth at that frequency.

The doubling time is the most portable number here. At twelve per cent effective, money doubles in about six years; at seven per cent, about ten; at three per cent, over twenty. Knowing the doubling time for a rate makes long projections checkable in your head, which is a useful defence against a projection that looks too good.

This is arithmetic, not financial advice. It tells you what the numbers do; it cannot tell you whether a decision is right for your circumstances. Fees, taxes and local rules vary, so check anything that matters against the actual offer and speak to someone qualified before committing.

Everything is worked out inside your browser. Nothing you enter is uploaded, logged or stored, which matters for the financial calculators in particular: the figures you put into them are nobody else's business.

• Shows value at the end, growth, money multiple, in today's money and doubles every together, so you are not running it twice
• Full year by year you can open and check
• Updates as you type, with no button to press and no page reload
• Copy the result in one click
• Free, no sign-up, and it runs entirely in your browser

The lumpsum calculator is used by writers, developers, students, marketers and anyone else who needs the job done once without installing software. Common cases include:

• Projecting a one-off investment or inheritance
• Comparing monthly against yearly compounding on the same rate
• Finding how long money takes to double at a given return
• Checking a growth claim against the arithmetic