How to calculate the monthly savings needed for a goal
✓ Verified in LibreOffice 25.8.7.3 ✓ Verified in Google Sheets (2026-08-30)Working backward from a target: what to put away each month to hit $X by a date.
The formula
| App | Formula | Notes |
|---|---|---|
| Excel (desktop) | =-PMT(A2/12,B2*12,0,C2) | A2=annual return, B2=years, C2=target. The 0 = starting from nothing; put current savings there instead if you have a head start. |
| Google Sheets | =-PMT(A2/12,B2*12,0,C2) | Identical. |
| LibreOffice Calc | =-PMT(A2/12,B2*12,0,C2) | Identical. |
How it works
PMT solves for the payment in any annuity — pointing its future-value argument at your target makes it answer the savings question: $20,000 in 5 years at 4% needs $301.66/month, noticeably less than the naive 20,000÷60 = $333 because growth does part of the work. At 0% return the two agree exactly. The minus sign flips PMT's pay-out convention into a positive deposit; a nonzero present-value argument accounts for money already saved.
Verified, not just documented
We ran =ROUND(-PMT(A2/12,B2*12,0,C2),2) in LibreOffice 25.8.7.3 (headless, with forced recalculation) and it returned 301.66 — exactly the expected result. We then ran the same formulas in Google Sheets, executed 2026-08-30: a formula-only workbook goes into Google Drive, which converts it to a Sheet and recalculates every formula with Google’s own engine, and comes back out as .xlsx carrying the values Google computed. It returned 301.66 for the worked example, the same value LibreOffice produced. Both engines’ numbers on this page are executed results. The Excel formula follows Microsoft’s official documented syntax — we do not run desktop Excel.
Functions used
PMT — see full Excel, Google Sheets & LibreOffice compatibility for each.
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