How to add up old money by hand
Old money sums work like any other, except that you “carry” at 12 and 20 instead of at 10. Add the pence column first: every 12 pence carries over as 1 shilling. Then add the shillings: every 20 shillings carries over as £1. Finally add the pounds.
For example, £2 15s 9d + £1 7s 6d: 9d + 6d = 15d, which is 1s 3d. Write down 3d and carry 1s. Then 15s + 7s + 1s = 23s, which is £1 3s. Write down 3s and carry £1. Finally £2 + £1 + £1 = £4. The answer is £4 3s 3d.
Multiplying and dividing
The easiest reliable method is the one this calculator uses: turn the amount into pence (or farthings), do the arithmetic, then convert back. Shopkeepers and clerks did it in their heads using tricks such as “a dozen at a penny is a shilling” and “a score of shillings is a pound”. That's why prices per dozen and per score were so common.
Who uses an £sd calculator?
Family historians totting up probate inventories and wills, local historians working through parish and overseers' accounts, students studying the Industrial Revolution, and readers of Dickens, Austen and Hardy who want to know what the characters were actually spending.
Common questions
How many pence were in a pound?
240. There were 12 pence in a shilling and 20 shillings in a pound.
Can I subtract amounts?
Yes. Switch a line's sign from + to − and the calculator takes that amount away. Negative totals are shown with a minus sign.
What about halfpennies and farthings?
Use the part-of-a-penny box. The calculator works in farthings internally, so totals with ¼d, ½d and ¾d are exact.
Why is my divided answer rounded?
Old money could not be split smaller than a farthing, so division results are rounded to the nearest farthing, as a clerk would have done.